Assuming Twitter and Spotify have equally poor formulas for monetizing music, my guess is Twitter views Soundcloud less as a profit generator and more as a lead generator. Since Twitter's revenue model hinges on ad impressions, the hope is Soundcloud could directly or indirectly bring more traffic into the Twitter ecosystem and boost overall ad impressions. Music is just a way to get users "into the store." Whether this is wise is a separate matter. Without knowing specifics about Soundcloud, the other attractive element could be that music is a natural activity on mobile devices. If Soundcloud sees great mobile usage, an acquisition strengthens Twitter's story that it is a leading media network for the mobile generation, which will play well with Wall Street.