I’m going to take charge of my life

I think it let's you mark the ball without hitting it

It creates friction between the cue and the ball to prevent it from sliding off the ball, it makes it harder to miscue. I've also seen people just use strips of sandpaper to lightly scratch up the cue.

Its helps if your new cause if you miss then it leaves the same color mark as the felt

It's for you to rub on the cue to look important whilst you pretend to have a strategy