Interesting thread. When I used to trim every 3 months - for the "full" blunt ends look that seems to be favoured around here - my hair never got past BSL. Obviously was cutting as much as I was growing, maybe more. Stopped trimming, hair finally grew out. It wasn't the only change I made, but I can't see that it hurt. I trim a bit once a year, but cut off any splits when I happen to notice them.