I don't trim unless I have too. I shoot brass in lots and usually in lots of 100. So if I have a lot of 100 pieces, that are either new or once fired from someone else, I will FL Size and trim, and usually don't need trimmed again until 2 possibly 3 firings. When I first started, I used to trim about every time. But you will get tired of that crap after a while, and only do it when you have too.

So when I start seeing my lot of 100 start going past max again, usually more than 10, I will start trimming. Usually after that, I toss brass when shot more than 5 maybe 6 times. But as always depends on the caliber.