1st round, I delete everything I know I will never use. My software also allows me to rate photos 1 to 5. So my first pass through the shots, from a particular event, is primarily: rating and deleting.
If I have what I need from the rated/processed shots, I go through again and cut deeper, this time deleted some good shots as long as I have a similar better one. Sometimes I also find that I don't have any 'good' shots of something I want, so I will rate something that didn't initially strike me as a keeper.
After I'm done working on that days work, it usually just sits on the disk; but every time I visit that work again, I normally deleted some more, especially if I find myself wasting time stepping through a lot of pictures I don't really need.
Truth is, though, I don't delete nearly enough. I have hundreds or thousands of shots that I literally have no need for (and nobody else will want either).
I used to be one of the "I don't delete anything" people, but I find that that just wastes time when revisiting old pictures. It has happened, only occasionally, that I have gone back to a set of old pictures and found a gem that I missed during the first set of passes through the work.