I used to sew over them all the time and rarely had a problem. Then I got my Kenmore and if I sewed over a pin it would break the thread at the very least. I got tired of rethreading the machine so I started taking them out. I had a teacher who said no, you are not supposed to sew over them but also said if you put them in at an angle they won't hit the needle. I try to put my pins in now at an angle just in case I forget to take one out. The only time I can't put them in at an angle is when I'm piecing and I need for two seams to match up. The biggest difference in hitting a pin, or foot or the sewing plate is that the last two cost more to fix or replace. Hitting a pin can cause your needle to bend and then ruin your plate; it's just not worth it.