I clip, it's just easier to me and my fiance was blown away at just how flat my quilt top ended up being. He even had me dig it out and show a few friends (before I put backing and batting on it) and bragged on just how flat it was while they looked at it.
Twisted seams are a big OCD/pet peeve problem for me, they will literally dig a hole in my brain until I clip them and I am a major grump until I do.