We know a bit they would drain the entire world of aetherWell, it also allows the raids to have more connections to the world. Or at least point out that there are other methods to taking down this villain that are smaller in scale but less likely to succeed. (Which is why I love the Icecrown dungeons and ICC.)
A lot of times, raids really are disconnected from the world and don't affect much beyond the area they exist in. This is probably why a lot more people like Binding Coil as we already know what would happen if Bahamut were allowed to come back. We don't know from experience what the goblins or Alexander would do. (That said...hopefully we'll see SOMETHING in 3.4 regarding that)