If you're able to get in say 2 targets out of 4 as early as possible, wouldn't that give you more time to scoop up the remaining ones? Liverpool seeem to be doing this regularly in wrapping up signings asap. Also you're looking at pre-season games to get your new player bedded in. You'll want that to be from the very first pre-season game to hit the ground running at the start of the new season.
I dunno that's just my logical understanding of it. Get signings in early, give then enough time during pre-season and start the new season on the front foot.