Pro: Barrel protecting lubrication when shooting lots and lots of rounds, as in prairie dog shooting.
Con: Needs to be cleaned out of barrel so that it doesn't attract water and rust the barrel.
Notice that moly coated bullets were a fad a few years ago and now that fad has almost evaporated. The reality is that most of us get no benefit from it. I don't use it because I don't see a reason to.