Basically it's like what a lot of games do to get cash, people go and download the apps and it gives you about 2 extra credits for paid apps and rating the app gives 1 credit It's basically for people who can't afford credits. Also a credit a day to get people more active and get on each day to receive more and more credits, and if someone gets on 7 days straight they get an extra credit!
It's good in theory, but easily abused. Spammers and disgusting pervs would have nearly unlimited speakers, they could just keep buying more instead of running out after 3-5. It would also decrease the value of ec, if all you have to do is turn the app on to get more.