In addition to globally controlling layer visibility with freeze/thaw and on/off, you can also control layer display in individual viewports with the "freeze in current viewport" property. (NOTE: You must be in paperspace or in an active paperspace viewport to use this -- it doesn't work in modelspace.) This allows you to show different aspects of the same model in one file, which you might need with demo/new plans, or partial/enlarged plans.
Back in the days of slow computers, the difference between FREEZE and OFF was very important. Freezing something allowed AutoCAD to ignore it during zooms and regens, so the program could work faster. These days, computers are fast enough that the time savings are very small, so the rules for whether to freeze a layer or turn it off have changed somewhat.
Now, I find it more convenient to use FREEZE for layers I want permanently off (say, architectural door tags), while OFF is for temporary invisiblity (like turning off rebar to hatch a concrete section).