I do it when my body feels like it eeeds it, which is everyday for my legs.
Having flat feet and being on concrete sucks. I end up rolling my hams, glutes/piriformis everyday.
I’ll do my quads and the above after a leg workout.
It’s fine to be used as part of a warm-up as it will increase blood flow to the area.
How do you get at your piriformis with a foam roller? I can’t even get at it with a ball.
I think you would sit on the foam roller and roll your piriformis (of the stretching leg) while having this type of stretch going on:
Obviously, your piriformis is directly on the foam roller. I do this, and the result is a lot more painful/helpful than simply trying to roll it through the glutes directly.
I hope this helps. If not, I think there’s a bunch of guys in SAMA who would do it manually for you ;).