These wader gaiters can be worn over your breathable waders to add that extra layer of protection from thorns and brush as well as protection from wear when crawling about stalking spooky fish.
And when you switch out the waders for wet wading pants (or shorts) these are great over top of the quick dry pants as well. Providing some knee padding and also acting as gaiters to keep debris out of the boots and providing a wet-suit like layer of warmth if you’re wading particularly cool waters. They also help keep you a bit more streamlined than wet wading pants alone for a bit less water resistance.
Quite a few Japanese tenkara & keiryu anglers wear these type of gaiers over the quick dry pants for fishing in Genryu areas(The most upper part of mountain streams).