It's to combat damage incurred when the valves get floated.
Lifters feel the play that has been introduced by valve float and adjust accordingly.
A valve may contact a piston top, a retainer might bottom on a valve stem seal, you might run out of slot length of rocker arm, or one of the springs stacks solid..........or you might lucky and experience it without anything breaking.
If you've ever seen someone overrev any 60s/70/80s small block and the engine stalls immediately after or runs missing on multiple cylinders like it's blown up..........but magically repairs itself after a minute or so, then you've seen someone experience lifter pump-up without incurring damage.
The reason you loosen them until they make noise and tighten them a specified amount, is to keep the lifters at the uppermost of thier adjustment range so they can only adjust up a very small amount.
The manufacturers are also assuming you adjust the valves at the published intervals to keep the noise down.
I've seen lifters that have a 3/16 inch range of adjustment capability.
Newer cars have rev limiters built into thier engine management so manufacturers are going back toward lifters nearly fully compressed to keep that service interval to just about never.........except lexus who screwed up and had to replace all lifters and valve springs in about 40% of the fleet sold from 2006 to 2011.
Lexus was using lifters near the bottom of thier adjustment but they had an issue with the valve springs weakening and allowing them to float below the rev limiter rpm for the cutoff.
They could have just sent out a new flash calibration for the ecus to lower the rev limiter 500rpms but decided that guaranteeing thier claimed horsepower important enough to replace all the valve springs and lifters.
Lexus claimed it was only the valve springs but I did compare the both upgraded and original lifters and found the upgraded lifters had much less range to take up slack.
