Alot of people will use the CUE button to keep in time when dropping their track, by tapping it in time a few times before switching and pressing play.
I use CUP as my play/pause button (instant/toggle). I always like hit CUP to play my track and use heavly when mixing out of a song when a drum loop is needed. And CUE (hold) to listen to my track and let it go to stop after i done previewing the track. I never use the play/pause, its not even in my mapping.
When mixing without sync, I find that releasing a button is much more accurate than hitting it, so I tend to use CUP to launch pieces with precise synchronization. Hold down the button until the moment is right, then release to trigger. No need to hunt and peck, also no need to even be looking at the controller as you can release with your eyes closed. It helps me pay more attention to the sound than to the controller.
It’s a personal preference, but I’m glad the choice is available.
Once I have found the part in the track that I want to start from, I hit Cue to drop a Cue point (rather than press set cue) and then as a few people have said I can press it a few times before I drop to make sure I’m in time.
CUP (short for cue play), I don’t actually have a function for in my current mapping but it can be useful if you want to juggle but don’t want that short “gap” between each button press because the track doesn’t stop playing when you take your finger off the button.