An even simpler example is page-based navigation. Can't register UI hits while pages are animating in and out.
What if you want to quickly flick through pages? Having to wait for each page to render would be awful.
Slider controls might be a better example, I think. In that case, the position reached by the moveable element is the data, and it is appropriate to take the value from the UI element (of course, if it lags noticeably, that is a UI design issue.) With slider switches, you could argue it either way, so long as program and UI remain consistent, but again there is a problem if the UI response lags the gesture.