Search:

handy if you go over a track that gets your wheels in the air and you cant get around it. lock em up, roll on over. generally means you can also take obstacles a lot slower rather than having a run...

if you want to spend serious money on diff lockers (looking at ARB for example) get some E-lockers, no air supply to worry about. for air lockers, would get yukons, cheaper than ARBs.