belts help with the "valsalva maneuvar".. such as during squats one SHOULD hold their breath during at least half of the conccentric movement, and the belt augments the tightening of the abdominal cavity to support the weight
i use the belt for heavy compound lifts to move more weight.. i feel its definetely beneficial
but i suppose using a belt too often might result in weaker core muscles than what they would be
Suffer now.. and live like a champion later.
Whether or not you can do overhead squats is largely irrelevant to whether you can back squat correctly. Most of the time the limiting factor in overhead squats is whether you have the flexibility and shoulder strength to keep the bar from drifting too far forward while held overhead. These factors have no bearing on your ability to back squat. There are tons of people who have very good back squat form and technique who can't overhead squat due to shoulder limitations.