Depends on the rifle and the load....
Through they years, having loaded and shot MANY loads, I have found that some rifles have at least two sweet spots with regards to powders and seating depths.
With this I mean that sometimes you will find that using the .020" you might work up through the powders load range and hit a very tight group right off the bat at the very lower end of the range, then continuing up through the load you will see another very tight groups on the upper end of the range. Call it what you may, nodes, sweet spots, or harmonics, the results are the same. I have also found that some rifles will have a similar reaction to seating depth, in that one seating depth will shoot absolutely great, but not function through the magazine, however seating it in sometimes by up to .125" off will hit the same sized groups with the same load.
I however do not do this with top end loads, and some powders, with out backing down a tad and working back up, just to be sure of pressure issues. In my daughter refurbished 6.5 x 55, I cannot reach the leades with a 160gr bullet and it still be in the case. However using the 140's seated to function through the magazine, and somewhere WAY off the lands, it will shoot outstanding groups out at 200yds with several powders.
Having a starting point is good, and I used to try and get as close as possible. Nowday's, I generally use the length which will reliably feed from the clip or magazine as fast as I can ranck them through. This is my starting point and I work my loads up from there seating deeper as needed. This way I know up front that no matter what my loads end up, they will feed with no further work on my part. As a side note to this, I have a couple of rifles which even though the round will slowly feed through the magazine fine with the plastic tip bullets, when quickly running them through as in trying to get off a very quick second shot, the sharper tips will hang up in the very tiny gap between the magazine and the bottom of the action. Seating them just .005" deeper fixes this issue. It was however not nice to find this out while in a hunting situation. Now I check several times using a dummy round to be sure of feeding before loading a whole mess up for testing.