It's tempting: I'm eager to get a project done, I feel like I'm in control of the fabric passing underneath the presser foot, and so who needs pins? That's where I have to stop and recall the agony of misaligned pieces and fabric catches, the overture to the drama of the seam ripper.
My sewing mentors have shown your humble servant how to pin effectively without overdoing it, and especially without destroying the sewing machine's needle -- and if you haven't broken a few of those as a soldier of the cloth, I'm told, you haven't earned your stripes yet. Madame Sherri admits she's particular about pinning; she'll put ten pins into a curve where three or four will do. I prefer to pin sparingly and intentionally in the manner of a championship boxer who throws fewer punches but lands more of them.
I probably do a lot of it wrong, pinning vertically when I should be doing it horizontally, on the wrong side of the fabric that will end up underneath the machine's foot, buried in lumps of fabric I'll have to dig out. I eventually get to them all, and I haven't broken a needle yet. Many people use pins to mark points instead of fabric markers. I've done some of that, but when a loose pin slips out as I'm wrangling with the fabric, I'm in trouble.
Sometimes I'll press my luck on a small item I can guide beneath the presser foot that won't slide around on me. That might have my Home Economics teacher gasping for air, but I think even she realized guys like to take shortcuts every now and then.