It depends on what I'm sewing. If there are seams that but up to each other and I want them to be spot on, I pin. If its a fabric or a seam that may need pins to stay put, I pin. You aren't supposed to go over any pins and some machines are worse than others about it. I had a teacher once who said to put your pins in at an angle and you'll never break a needle on them. I try that (except for butting seams) or try to put the pins down far away enough from the seam allowance but close enough to do the job.