It's a good way to determine sort of a worse-case max pressure. Meaning if you build a max load OFF the lands, then it somehow ends up in the lands (loading mistake, powder pushes bullet out) you could have problems. If however you find max pressure touching the lands you know you have found a max that's hard to screw up. You can always back off the lands from there. Massive powder compression excepted.
It's not that often that being up on the lands shoots best for me. When I've messed with TSX's in a few rifles they most assuredly preferred being well off the lands.
