I am going to go against the grain on this one.
We have a 2wd F250 7.3 and it had a posi-traction in it from the factory. We were always getting stuck in the sand and lose dirt as a posi will slip if enough load is put on it. Along with being at 7,800#s, I guess getting stuck in sand is to be expected.
When it got to 240,000 miles I decided to rebuild the diff with new seals, bearings, gears (changed to 4:10s from 3.73s) and at the time it was cheaper to install a Detroit locker, a mechanical locker, and always drives both rear wheels. We hardly ever get stuck any more and we have always been able to recover ourselves with the four our "tred" recovery bars we have on the truck.
So while having a winch is nice to help others - if you have a locker you yourself may not get stuck as much and you should get a set of recovery boards anyway. The hassle factor of using a winch especially if you're in the sand or mud with no trees are around is just a pain. Where if you have a locker in the rear you may - most likely would not have gotten stuck and need the winch anyway.
Depending on your stock 4x4 setup in your vehicle you may at best only have 2 wheel drive when in 4x4 mod, one front wheel and one rear wheel. So with a locker in the rear you at least have an honest three wheel drive at all times.
Another thing to consider in that when helping someone else your first go to piece of recovery equipment should be a snatch strap for ease, hassle factor and safety.
Just my $0.02s.