Always a site-specific thing. That's why you have to experiment to find out. I have a section of very rocky ground that is a steep south-facing slope (gets direct hot dry sun of summer) that was clear-cut over 20 years ago. It's still thick and nasty. Then I've got north-facing slopes with better soil that were just cut 2 years ago and the regrowth is well over my head.I think three years would be too long in some areas. I have one half acre area I mow annually because the willows want to take it over. A 44hp tractor with a 6' mower tends to bog down in spots despite mowing annually.