For those who hold by wearing a gartel for davening (for separating the upper and lower body), is it necessary when already wearing a belt?
Halachically there is a requirement to have a separation so that one's lower half is separate from their heart. This is taken care of by wearing pants, even without a belt, as the pants form a clear distinction. Another reason to wear a gartel is to prepare oneself for prayer. The Kohanim used to wear a gartel as part of their avoida, and today prayer is called avoida shel lev, and so in that sense many have a minhag to use the gartel to help change one's mindset when approaching davening.