If you're doing a drawing app, then 120fps helps you keep the stroke close to the stylus. Even then it may lag a bit because of a few frames of GPU latency and you have to do predictive stroke points and then adjust your stroke later. See https://developer.apple.com/documentation/uikit/touches_pres...

Similarly, if you're dragging something around with your finger, 120fps keeps that thing closer to the finger. Just improves the UX.