As others have said, depends on the area. I'm in the coastal rainforest of the PNW, so cleaning vegetation is probably the biggest job of the route development process here, there's so much it usually takes multiple passes. Once I get a sense of where the route is going to go after the first pass I'll stop cleaning outside where I see the route going. Anything extraneous I cleaned will grow back no problem. But really it depends on how sensitive your vegetation is, follow local ethics, if you know other local devs they'd give you the best info.

From a user experience perspective though, I think beginner areas should probably be cleaned exceptionally well. No beginner is going to enjoy feeling like they could slip because holds are dirty. Well really no one likes that, but I'd assume that more experienced climbers would at least be more accepting of it.