1) if you want UI visual response to be perceived as instant, you'd like to aim at 100ms or below - and you can't draw a response that fast if your code only gets the input signal 101ms after the actual physical touch.
2) if you want audio cues (say, a click sound when clicking a button; or app that plays drums/piano/whatever), then the noticeable latency is even lower; if you have to approach 100 ms then it will sound disconnected from the actual touch.
3) A common platformer or fighting game running at 60fps has 16ms per frame. If there's a 100ms input latency, then the action (say, jump or block) happens on a game world 6 frames off from what the player saw when doing that action; which tends to be too late. Only pro-players worry about single frames; but any average player is affected by 6 frame difference.
For input devices - keyboards, mice, gamepads, whatever - the acceptable latencies (not good or great, but barely acceptable) are measured at tens of ms, tops. A 50 ms difference is not tiny, it's huge.
1) if you want UI visual response to be perceived as instant, you'd like to aim at 100ms or below - and you can't draw a response that fast if your code only gets the input signal 101ms after the actual physical touch.
2) if you want audio cues (say, a click sound when clicking a button; or app that plays drums/piano/whatever), then the noticeable latency is even lower; if you have to approach 100 ms then it will sound disconnected from the actual touch.
3) A common platformer or fighting game running at 60fps has 16ms per frame. If there's a 100ms input latency, then the action (say, jump or block) happens on a game world 6 frames off from what the player saw when doing that action; which tends to be too late. Only pro-players worry about single frames; but any average player is affected by 6 frame difference.
For input devices - keyboards, mice, gamepads, whatever - the acceptable latencies (not good or great, but barely acceptable) are measured at tens of ms, tops. A 50 ms difference is not tiny, it's huge.