Sure, a locker is not 100% required, but there are some areas I have taken my truck where I had a wheel in the air, and the other three on the ground. The adjacent tire would just spin. I also know that in the rain, the limited slip in my truck makes the truck fishtail a lot quicker then an open diff. A friend of mine was parked on the side of the road in his 4x4 excursion. The two driver side wheels were on pavement, and the passenger side wheel were in the dirt/mud. He put it in 4wd, and the passenger side tires just kept spinning and didn't go anywhere. I guess if you have enough weight to overcome any traction issues with the HP output, then the locking diff would not be all that helpful.