Well, Playing devil's advocate, you think you could apply the same Theory does taking ice baths post training. Ice baths cause everything took entrapped and in theory squeezing out lactic acid and toxins and all that shit and whatever else.
I dunno... from a performance standpoint I can see them helping the same way wearing a bench-shirt (or even just a tight tee-shirt), even if it's just psychological.
Personally I can't stand the shirts, as I feel like I'm being choked wearing one. I do wear compression socks occasionally, especially at night.also Gotta few pair of red over-the-knee soccer socks (made by UA, just so happens), that aren't meant to be compression socks but they sure do feel like them. They're XL mens, but I have no clue how anybody would manage you get these stretched over top soccer shin guards no matter how much fucking baby powder you used.