It depends on where you get your meat. I buy all of my pork butts at Sam's Club and they all have a perfect 1/4" fat cap, so I have never touched them.
If your butcher/market leaves a lot of extra fat on, I could see trimming "some" off. You just want to make sure that there is a good 1/4" or so of fat cap left on.
I have rarely seen a pork butt, even when I have purchased from other places that required any trimming.