I can't prove it, but feel like I am able to walk closer by deer at that time without spooking them as I would with a light earlier. To me, the real key is all the bird noises that cover your sounds. Another thing I like about this method is that you can see the trees better and pick the right one to climb without shining a light all over. I do not usually hunt a specific tree on public, so I also have to find one quickly and thus it allows me to do that and avoid poison ivy and other hazards. He also taught me not to worry about bumping deer going in like this, odds are if you went in early, they would be gone by shooting light anyway. He killed a lot of deer, so I listened.
Worry and stress should not be part of hunting, we do this because we love it and it is supposed to be fun. If you are late, so be it. If you bump a deer, it didn't leave your world forever, and even if it did, there are others out there. If you're not having fun, go home and come back when its fun again!