It depends on what kind of litter you use, and how quickly your boxes get dirty vs. how often you have time to scoop.
If you can scoop at least once a day the method in this link has worked really well for us to keep odor down:http://www.catinfo.org/litterbox.htm
If you don't have time to scoop regularly, it might not be good because the cats may break up the clumps of used litter as they dig - in that case, I'd go for a thinner layer and dumping the litter & washing the box every week.
We more-or-less use the video method but use Fresh Results corncob-based litter by 8-in-1 instead of clay, and use 18-gal Sterilite bins as litterboxes instead of covered boxes, to help keep the litter inside, and we spray the boxes with this litterbox spray
to prevent sticking before filling the box with litter to 4-5 inches deep.
I spot-clean the edges if the cats soil along the edges or corners of the box, and respray cleaned areas with the litterbox spray (but not on the litter, because I'm afraid it might interfere with clumpability). I try to scoop twice a day (at least once at a minimum), and add litter as needed to keep the level high.
Every couple of weeks I'll sift the litter with a fine sifter to get out any soiled bits the litter scoop might have missed, and pour it into an extra box after spraying it with the non-stick litter spray. Then I'll wash the used box out, dry it, spray it with litter spray and repeat the cycle with the other litter boxes.
Eventually the litter will become soiled and I'll change it entirely, but sifting the litter and cleaning the boxes helps stretch out the life of the litter. It's a bit more expensive to fill the box so deep in the beginning, but it seems cheaper in the long run because I don't have to dump the whole box & start fresh every week.