Oh, and if manual or limited lockers were installed, does that mean the "high" and "low" buttons on the dashboard of our truck is rendered useless?
Or the floorboard mounted lever, if so equipped?
No, no traction aid has any impact on high and low range. They simply adjust which wheels get the full torque.
Open differentials transfer all the torque to the wheel with the least traction. This is great for almost every on road condition.
Limited slips are an open differential until it senses a drop in traction, then it transfers torque to the other wheel. These all differ by design and some are torque biased meaning they transfer torque 70/30 or 60/40.
A full locker transfers torque 50/50 to each wheel. When turning, automatic lockers like the Detroit will unlock, allowing differentiating wheel speeds. Spools and welded diffs, along with the manual selectable OX, ARB air, and Eaton E-locker are locked all the time when engaged, no matter what. The selectable lockers can be turned off, leaving an open differential.
The reason limited slips are so popular is they are very street friendly, yet provide excellent offroad traction. Tru-tracs are very popular because they are extremely durable. They are gear driven, as opposed to clutches or springs like many other limited slip / posi-trac units.