Seems to be this bizarre idea about having a strong bench to effect the game later.
I remember Stuart Pearce talking about it when he with Moyes at West Ham and how now it's a squad game and your bench is as important as your starting 11 because they're the players you can use later to change the game. I think the fact him and Moyes are out of a job now is a good indication of there being a problem with this kind of thinking.
If you've got 25 players of equal standing and ability then yeah, fire away, be tactical with your setup. But if you have clearly better players for the job then put the best 11 out that you can, and maybe you won't have to use your bench to affect the game as much later on. And if you do, you make do with what you have. Don't hinder your starting 11 on the premise you might have to change things, not even knowing at that time what those changes will need to be.