I started using them mostly for the cold weather (Janjis). It's been a revelation. Previously, I'd wear "normal" pants and would always feel somewhat cold at around 0C. Janjis have been perfect for that and lower. They're light compression, for warmth.

I also like how they feel. They're less distracting than normal pants.

As for recovery, I do wear them (or other more recovery-oriented leggings) after hard runs. I think they help; I haven't felt sore on my legs in a while. But it's hard to say if it's just because of the pants; I might just be used to it.

Finally, I haven't felt a difference in performance with performance oriented leggings (2XU). I know they're supposed to work, but I haven't proven that yet. Haven't ran a long (half+) race with them yet to be fair.