Last year, I recall some rules on deployment. Each player was given a deployment zone. Anything placed on the table during initial deployment had to go within that zone. This restriction did not, as I recall, apply after the game got underway. Units with deep strike, flank march, flyer and other similar rules could show up anywhere their rules allowed. Reserves could march in from any friendly table edge.
I can see a reason for this sort of rule. If all a player's models are together, and the player stays near his models full time, speed of play is improved. If everybody scattered their models all over the place, it could get very confusing.
At the same time, having reserves free to reinforce where they are needed seems an appropriate part of the game. Much would be lost if reserves can't be brought in where they are needed.
I'm entirely content with how this worked last year, but thought I'd mention it now.