This whole idea is one of those things that some benchrest shooters do for optimal accuracy, so regular shooters figured it must be the thing to do also. Benchrest shooters will often jam the bullet into the lands, or just barely touch the lands, or back off 0.010" the lands, or whatever they have found to work for them. So naturally, a lot of folks have decided that 0.010" or 0.030" or 0.050" or some such figure is a magic seating depth.
Varying the seating depth can and will have an effect on accuracy, no doubt. But so will the amount of powder you use. They both have an effect and you can tune your load to your rifle using either or both methods. What I typically do is decide first what COAL I want. It might be industry factory standard length, or in a few cases I have taken the trouble to figure out what OAL I need to seat the bullet 0.010" off the lands. Whatever you decide, go through the OCW procedure of varying the powder weight in increments of 1% and shooting them in round robin fashion.
When you find the magic powder charge for your bullet/powder/OAL, then you might want to play with increasinig or decreasing the seating depth in small increments. Typically though the seating depth won't change the accuracy very much if you have found the right powder charge.
