Rats do not need them, nor do they need the mineral blocks if they get a balanced diet
But they need iodine Iodized salt is the primary source of iodine, and the only other sources are seafood, plants that were grown in iodine-rich soil and some dairy products. I would think I would be better safe than sorry when it comes to guessing where my plants are grown and whatnot. And my rats don't get fish ( I hate seafood blah ) So I'm going to stick with the salt licks

The rats don't seem to appreciate them much unfortunatly...
I put one of them in Icarus's apprent "peeing spot" and I had to throw that one out