I usually go every few months. I don't really have a time line. I stuck with the same cut for a long time after trying to change multiple times and hating my haircut! I have healthy hair so it doesn't get split ends too quickly.
I'm also guilty of not going to the same person every time. I live across the street now from the woman that has cut my hair since I was 5. I noticed when I got the worst haircuts from her was always right after she heard someone had passed away and she was going to have to go to the funeral home to do their hair and makeup, so if we found out something like that had just happened, we would leave and go another day! She does a great job for basic haircuts and obviously knows how my hair behaves! And she's still cheap, $15 for a wash and cut and she doesn't charge extra for a blow out... just does it if she has time. Of course I tip generously. Another is my boyfriend's cousin. I've only been to her a few times, so we're still getting to know each other I think. The expensive one is who I go to when I want a more stylish cut with layers and such.
A few days ago, I had a ton chopped off. My neighbor said I could have waited 3 more months and would have been able to donate it, but it's just too hot here to wait! I was tired of wearing it up all the time.
When I can post pictures, I'll post a before and after. I found a great website that helped me pick it. There's a more "stylish" one I like, but I wasn't sure about going that short yet!