(POINT #1) Actions can be performed at maximum efficiency (with no "dead time") by buffering.
By buffering a move, the "dead time" between the end of one action (attack or dodge) and the start of the next action is now eliminated because the next action will take place immediately after the previous action has completed. Before the 0.39 update, it was necessary to wait until the end of the current action before the game would register your next input. (Unless you had absolutely perfect timing, this caused a slight delay between moves.) Now, you can input your next action anytime during the ongoing attack or dodge. Note that this is not a change to the actual speed of the action but simply an elimination of the unused/free/dead time between actions.
Analysis of impact on play:
-Although slight, you could say that damage may be applied and battles won a little bit more quickly due to the elimination of the downtime. For example, the turnaround time between dodging a charge move and hitting back with a charge move of your own can be reduced by buffering your charge attack immediately after initiating a dodge--unless, of course, you were "frame perfect" before!
-It may feel like the game "eats" fewer commands because the window to perform an action (which used to open only after the completion of an attack or dodge) is now open earlier. In addition, the window to perform an action at maximum efficiency, which used to be only the split second after the end of an attack, has now been extended much longer to cover the full duration of the previous attack.
-Quick moves may now feel even faster because they can be be unleashed one after another with no delay as long as you buffer them before the end of the current move.
-It may also feel easier to hit charge moves: before, you had to time the charge carefully so that it would not overlap with a previous move, whereas now it is "easier" to hit the charge move since it can be buffered in advance. With dead time between moves eliminated, you may also feel like multi-bar charge moves are more useful as well because less time will be wasted.
-The maximum theoretical DPS of a move may now feel easier to achieve, although it is still subject to the use of dodges, "overkill" from charge moves, waiting to see if a charge move is incoming, and similar issues.
(POINT #2) Buffered actions cannot be undone.
Once you input an attack or dodge, it will automatically be performed after the current action is completed.
Analysis of impact on play:
-Button mashing is now severely punished, as it is now impossible to dodge if you have an attack buffered. Although you can aim for maximum efficiency with buffering, even one extra tap will make you unable to dodge an incoming attack! To this end, if your play style was to tap/attack aggressively and only stop when you see a charge attack coming up (thanks, u/vibrunazo!), this style becomes less viable now that the game will use those extra taps to lock you into an attack much earlier than before.
-This inability to take back buffered actions may make it feel harder to dodge in general because you can no longer react if you have already buffered another attack in advance. For some play styles, this could make it feel riskier to train with a pokemon that requires perfect dodging in order to win.
-The game may feel more sensitive to stray taps, as they will cause actions to be buffered when they would previously be ignored (during an attack or dodge). It would be fair to say that it is easier to attack one too many times and miss an important dodge, particularly if you are used to button mashing, because the longer window to input moves is also a longer window to accidentally input moves.
-On the other hand, some may feel that the game is actually easier to play at maximum efficiency because it is less dependent on fast reflexes and more on counting attacks between dodges, with a longer window to initiate each action. The bubblestrat, for example, may be performed more reliably now that it is less subject to precise timing of attacks and does not require dodging. Similar play styles that incorporate no dodging at all may feel easier to execute as well.
(POINT #3) Only one action may be buffered.
The next move following a buffered move will only be registered after that buffered move has started, so multiple moves may not be buffered in advance.
Analysis of impact of play:
-This affects the overall rhythm of the game by fundamentally changing when it is necessary to input an action. Where the previous ideal time was "as quickly as possible after the last action finished (but not before it ends)", the new ideal time is "anytime after the start of the current action (but not before it begins)."
-You could argue that more overall awareness (and especially discipline) is necessary during battle because while you will likely make fewer inputs, the timing of each one is more important than before. Instead of mashing 10 times to hope that one of your taps registers right after the end of a move, you have to make sure you attack just once (and not twice) if you think you may need to dodge an upcoming charge move, for example.
-In contrast to point #1, although the window to hit a move at maximum efficiency is actually longer (with the full space of the current action now available instead of the small space right after an action finishes), the limit on buffering may actually make it feel like the game eats more moves depending on your play style. This is because the change from the old system is so significant that you may fall into a rhythm of not only inputting attacks when you don't want to but also failing to input attacks (and especially dodges) when you do want to.
(POINT #4) Summary and other issues
Generally speaking, I think you could argue that the new battle system gives more opportunity for maximum efficiency (making some battles "faster" or "easier" for some play styles) but is extremely unforgiving of extra inputs (making other battles, and especially critical dodges, "harder" in some cases as well). Overall, I'm quite excited about the changes, but I can certainly understand some frustration as well!
Finally, since I haven't been able to research beyond this on my own, I'm curious about any other impacts of the new system. For example, I imagine that the buffer system makes players less subject to missing dodges due to input lag on older phones or weaker signals, but I'd love to hear about your experiences in the field. Let's see if there are any other issues out there as well!
- Buffered actions can carry over into the next battle in a gym as well. If you're using the bubblestrat and don't want to be destroyed by the next pokemon in line, do be careful to count your attacks!
- If you queue up a charge attack and your pokemon faints before it goes off, your next attacker will use a charge move right out of the gate!
- The "nerf" to constant attacking and stopping only when you need to dodge a charge attack! Indeed, this particular style becomes more difficult (perhaps no longer viable in some cases?) now that the game will take your extra inputs to queue up extra quick attacks.
- Dealing with the new system: "You only need to tap once near the end of your attack animations, and when you know a charge is coming, lay off for half a second to dodge it."