The advice I had been given about lockers is to install them on the heaviest end of your vehicle if you only use one. Effectiveness is lost if it is on the lighter end.
The only time I wished I had a locked front was when I backed my empty truck into some muddy goo that made the rear limited slip differential useless and the front differential allowed only one wheel to spin. I couldn't get any momentum and could not rock out of the goo (just sank deeper). A small tug to get some forward movement was all I needed to get out.
I drive buggies with locked rears which have severe understeer unless you goose the throttle in a turn help break one rear wheel loose. I don't think you would want to drive this way with your TC on board, so I would not recommend a locker on either axle for the loads we carry.