As for protecting the gun. Most guns probably don't need them. However I've seen it said more than once not to dry fire some older firearms, Colt revolvers come to mind. If you plan on dry firing a lot, they are cheap insurance. Like many other preventive measures, it can be hard to prove their worth beyond anecdotal evidence. That doesn't mean they aren't helping.
MSgt, USAF, Retired
NRA Life Member
The hardest thing to explain is the glaringly evident which everybody had decided not to see. - Ayn Rand