Basically if you grind wins you will always choose modern in duos for example, if that's not available you will choose library. The problem, it's much faster to choose maps at the top of the list than down a few spots and because of how the ordering system works right now, alphabetical order depicts what map is on top. By being able to re-order maps, you can put bad maps on the bottom and your favourites on the top. Not a huge change but it's an improvement imo
