I guess I am not getting it on the issue of setting headspace "TIGHT" What is gained by doing this. I read on a post where the poster said he was going to set up a new build that way so that he would only need to bump his shoulders back 1 thousandth of an in.

What is gained by doing this over setting "normal" headspace and still marginally sizing your brass.

Hate to sound ignorant but this doesn't make sense to me.