While some may see that is a positive, I know many people who dislike it. The people I know who disable or limit which accounts can be used is simply for the fact that it's annoying when you're on your computer using iMessage but your phone still receives the message because the iCloud server doesn't sync fast enough.
That's a separate issue. That's just iMessage having ridiculously bad servers and/or server software. There is no excuse for a message that should fit in one TCP packet taking 10 seconds to send.