just general stretching of quads, hammies and IT bands after working out (especially running) is beneficial i think.
I lie on my side and put the roller under my
outer thigh : then I put all of my weight on it and proceed to roll back and forth. It is a hard foam, therefore it hurts like hell when you press it against tender/tight muscles! Feels great afterward.
Can be used on any part of the body, you just put the roller under said body part and roll around until you feel it is pressing against a tight muscle, then work it out!
You can buy them at target for $20 but I have only ever tried the ones at my gym, so don't know if they differ between brands.