My rule of thumb is to go down a hill with the same number of lockers on as you used to go up it. Same gear too, or one lower if needed. If you're talking steep off-road downhill sections, then yes, you shouldn't need to use the brakes much at all if you have the right gear, but you I would say you can use a gear to prevent gaining speed if you are going slow enough, it doesn't tend to help you scrub speed. So say you are in second, and still gaining speed, at that point I would not just shift to first, I would slow down considerably, shift to first, then ease off the brakes. If you keep gaining speed them you are geared too high, or just have too small of an engine possibly to hold your speed.
When I am going down steep hills I am usually in 4-low, 1st or 2nd gear and that keeps me around 3-6mph. That said I have had trucks that just didn't have enough engine braking or a low enough gear for that to work. That's actually how hill descent control got invented according to a story I heard once, Land Rover was embarassed that one of their new models of soft roaders wouldn't control it's speed well when following their Defenders down hills, so they asked their engineers to come up with a fix (it didn't have a transfer case with a low range) so they made hill descent control.
Also, if you have that feature, use it.
