Never, never, never sew over a pin. If you hit one, you could (1) throw your machine's timing off, requiring a costly trip to the repair shop or (2) break your needle or the pin, possibly causing the broken portion to fly up and hit you in the face. I know women who have had both happen to them. If I pin, I usually pin from right to left on the edge of the fabric. That way, I can pull the pins out with my right hand without having to stop, though I do slow down.