The locker (detroit), were talking in front axle, will only engage when recieves torque input. Which would be about any time you are trying to get traction with front end. The thing about the detroit versus all others, is that is simple and effective, and fact is an ARB acts just like a locked detroit when you have it engaged, so the only real benefit is to be able to be in "four wheel" and only getting traction to three wheels once crap starts spinning (assuming the rear is locked), thus equating to ability to turn. I say go with a detroit, and just disengage "four wheel" if you need the steering. This is the age old argument. The huge drawback to a detroit is on ice or snow, where handling can get squirrely if trying to drive on roads with snow. Just my 3 cents worth.
If you ain't hurt, you ain't playin' hard enough.
The General