Auto Locking Hubs explanation

Ok Ive gone through a lot of threads here and cannot find an answer to my question.

I have a 2001 F250 7.3 Diesel. I just replaced both auto locking hubs and wheel bearings. All tested fine and according to my mechanic, all is working normally. I want to know if 4WD low engagement is the same as getting out of your truck and locking the hubs manually. If I have my hubs in the "auto" position, why do I still have to get out and rotate the hubs into manual. Some people are telling me that because of limited slip differential that I dont have full 4WD until I get out and change the hubs to manual. So my question is why have auto locking hubs if I still have to manually change the hubs.

It seems like I have half 4WD until I lock the hubs myself. Then its great. I've gotten stuck in snow many times thinking I have engaged 4WD when I haven't.
Its frustrating when everyone with 4WD is just plowing past you.

Thx anyone

wopr21