I used to wear a belt no matter what bodypart I was training,I practically slept in the damn thing.
I think most guys from my era always wore a belt no matter what.
These days,I put one on only when going extra heavy on legs or deads or anything that might strain my injured lower back........usually rowing movements or deadlifts only.
They used to be part of gym fashion influnced no doubt by the muscle porn mags which probably explained why so few looked worn in with years of use
Im not dismissing them, I had a few but gave some away when I realised how little i needed them