Better looking maps = new players playing the game rather than quitting off looks
Smaller amounts of maps played (hopefully, assuming ranking comes out making people wanting to play maps that affect ranking more often) = new players learn new maps easier, don't get lost each time they open a server. (I only played Syncmasters cable when I started, cause ub_cliff was the only map I knew, getting lost isn't fun).
Teams using the official maplist to match = teams focusing on improving on specific maps, rather than moving to new maps. Hopefully in the long run makes teams actually need teamwork to win, since there will be no map advantage.
I don't see any downside. I argued for this before, most people were against it. Most games don't have as many maps as DP has. That's why DP matching requires no real communicating other than recon. It'll increase competitiveness, it'll lead to better things like stats/rankings, it'll help new players learn the game if it's on pub servers, it'll make the game have nicer quality maps that most mappers are to lazy to do themselves.