I provide a salt lick for all of my rabbits. Some of them use them, some don't.
In most cases, the sodium that a rabbit needs each day, they will get from their pellets. Some pellets don't include the sodium though. The only one that I'm aware of that doesn't, is Sherwood Forest, so a salt wheel is needed when feeding that pellet. So just check your ingredients and feeding instructions on the bag of pellets that you feed. Also a rabbit that tends to drink a lot of water, may have a higher sodium requirement.
I figure it doesn't hurt to have it in there. If your bun doesn't need extra sodium, it likely won't use it.