I don't use the rear lock for normal driving, but it can be the difference between walking out of the mountains (or spending hours getting unstuck) for off camber snowdrifts with a steep drop off / truck's at a steep angle (the kind where you are almost shitting your pants and pray you keep moving toward the far side), getting through a deep swale, sand, etc. I never keep it locked in except to get through tricky spots that I damn sure don't want to stop moving. There have been several times where it's the only way I could continue further.
Sometimes I miss my 68 chevy with a 327 and pizza cutters, all this traction control crap that people "think" they are turning off with the push of a button annoys the crap out of me. Reaching to lock in 4wd while in the cab on a shitstorm day makes me appreciate my F150 though. :)
(removed the running boards and that stupid front plastic spoiler thing under the bumper that just pushes snow/slows the truck when it gets deeper)
For sure, I remember feeling unstoppable in my friend's Land Cruiser in high school.