I am afraid I am at a loss as to what to say to the people who state "I sew over pins all the time, and haven't had a problem" or something similar, it's like saying I have driven for years and never had an accident, umm fingers crossed! You haven't had an accident because you are obviously a good and careful driver and as for sewing over pins and never had a problem you have just been incredibly lucky!
I felt so sorry for one of my pupils who ignored the advice I had given her about sewing over pins and using the best of needles, changed often. At class one week she put in a new needle, cheapo supermarket one, and started sewing, a minute or so late there was a terrible clunk from her machine and before I could stop her she had tried to sew it again, another terrible clunk. Short story version, she had completely massacred a pin she had sewn over which in turn massacred the bobbin timing, a new £400 machine was ruined.
Knowing what sewing over a pin can do I don't see why you leave them in as I cannot see any advantage in doing so, I am not trying to be rude or impolite to anyone I just don't see the point!