When you have a "friend" whom you call for immediately gratifying hot sex, but there are no strings attached. After a hot "work out" session, one or both partners will remark, "Oh God, I really needed that!!" Hot sex is excellent stress relief therapy, and to have a partner aware and in need of this scenario can be highly mutually satisfying.
Married woman to her therapist, "I am so glad my stress relief partner was available last night. I feel so good today!"