In a less murderhappy court, it's alos a a way of chipping away at the Emperor's influence. Impeccably propose a socially excellent match you know he'll refuse, and he'll have to spend time and political capital impeccably refusing. Meanwhile ,other noble houses will realize "Oh, the proposal option is open now?" and they'll send proposals as well, and at least some of these are going to be allies of the Emperor who he's going to have to be more careful not to outright snub.
And of course, there's also the (remote) possibility that he /does/ accept one of the potential bridegrooms, and if it was one of the ones you carefully selected, you've got a hook into the Imperial Family.