belts are ONLY for trunk-loading, structural exercises done near maximum weight, i'm talking 95-100% of max.
1) if you're using a belt when doing your 5-12 rep range squats you're only setting yourself up for disaster by getting your core used to not having to do most of the work.
2) a big reason for a belt is to prevent back hyperextension... to do this it has to be worn VERY tightly. if you are walking around the gym wearing a belt throughout your entire routine you are A) not wearing it correctly, and B) using it for all the wrong exercises, so you're C) COMPLETELY CLUELESS
3) as stated above... belts are for trunk-loading, structural exercises involving possible hyperextension of the back at near maximal weight. what does this mean? olympic lifts. unless you are doing olympic style powerlifting e.g. clean and press, clean and jerk, hang clean, etc. etc.... you probably do not need a belt.
I work as a personal trainer and am in the gym 6+ hrs each day. I honestly doubt if i've ever seen a single person ever wearing a belt for its intended use. so sad.