Why are you always doing DL for sets of 10? Probably don't need a belt for a weight you can do for ten if your form is good. Your probably limiting yourself a bit by doing such high reps all the time if your goal is to add weight to the bar.
Some poeple NEVER use a belt and DL insane numbers and do fine. Others swear by them. Depends.
Personally I only use a belt for top sets. I didn't start until I got into the 500's, but that doesn't mean everyone should do the same. I would definatly use one for 1RM's, but again, some do not and do fine.
Honestly this Q has probably opened a can of worms.