From what i understand, some teams tend to stack sites when they don't have a good chance to win the round if they play normally, this is when they have worst guns (eco, bonus), so that if the other team comes to their site then they might have a good chance to win it. Not all teams do that but its a good way to maybe take control of a round that you are more likely to lose. (They are pretty much gambling so its pretty risky to do it in a full gun round).

looks pretty cool, but i don't think teams would stack sites as much as they do in the simulations. Im really excited to see how it becomes in the future tho!