If your cat is absolutely an indoor cat, and there's no chance he'll get out, then he doesn't need a collar, IMO.
My cats are all indoors, and don't have collars on them. I only put them on when I take them outside for whatever reason: vet, travelling, etc.
I was so freaked out one day when Mozart got his collar around his jaw trying to get it off. That's when I took all their collars off.