I took an off-road class last year and the instructor used a JLR to demonstrate the BLD system and showed by climbing rock stairs, that it does as well as using the lockers when one wheel is not contacting the ground.As far as I know, there is no way to disable BLD. Holding the TC button for 5 seconds disable's the Electronic Stability Control (ESC).
It really works!!! This summer I was on a 2 track and the road was blocked, so I had to drive up an embankment to get around a tree. My front right tire was in the air spinning with no traction and both my back tires were just digging in.
After a few seconds, the BLD kicked in and power was sent to my front left tire. I literally shot forward and climbed over the embankment. After that day, I've became a true believer in the BLD system.