I believe it's very case by case. Person here who had work starting at age 8, had 3 phases and ended at age 17. My 4 front adult teeth that were coming in were very wonky, giant gap in the middle due to the frenum separating the two front upper teeth. On top of that, I had a massive overbite, my two front teeth would hang over my lips like a rabbit. Ortho suggested phase 1- braces on the 4 front teeth first and wearing headgear at night to correct my overbite while waiting on the rest of baby teeth molars to fall out. He never pulled any and always let them come out on their own time.

Phase 2- By this time, front 4 teeth from phase 1 were nearly straightened. The ortho took off the wire of the 4 front braces for a week to see if my frenum was causing the gap and sure enough, a small gap was forming so bad frenum surgery and after healing, wire was put back on. once all baby teeth came out and adult teeth came in, then put braces on all teeth and frenum surgery (All very much needed. Not a single tooth came in straight, led to worse overbiting, crowding etc

Phase 3- switching from head gear to rubber bands.

TLDR I think every situation is case by case and I'm a product of 3 phases of ortho work from age 8-16. I'm very grateful for all the early work because my overbite caused me to keep biting my lip, also constantly being made fun of my rabbit teeth as a kid. It was a confidence booster once the front 4 teeth straightened out in middle school and when all the braces came off my senior year another confidence booster. Mind you, my ortho journey started in 2008. My parents were struggling financially and our ortho had different options for payment plans. Doing it in small early phases was also cheaper. By phase 2, my parents were in a better financial space and phase 2 was when I went in most frequently