What exactly are topical steroid gels used for?

Better absorption & I am assuming you are talking about sex steroids like Estradiol or testosterone. Fewer side effects are likely, because they do not go through the liver first. If you are talking about corticosteroids, the medicine is on the skin at a higher concetration, sparing the body of steroid aside effects. They are used for inflammatory skin issues. Most forms are creams and ointments, not gels.