I've taught at two schools here in China, and have never truly understood why E.C.s exist. I've found that running an English Corner is more closely related to being an entertainer.

English Corners are an opportunity to practice English in an informal atmosphere and environment. It is something like using "living English" outside classroom. Once you have learned the basics in a more formal classroom setting, you can actually only learn a foreign language by using it, by applying practically what you have learnt. The classroom is a more artificial environment that makes it more difficult to imitate real-life situations in which to use and practice the foreign language. Hence,
providing opportunities to practice a foreign language more freely in less formal environments outside the classroom is a must and a good idea.

Whether the way to do this by means of an obligatory English corner is a good and efficient one is something I would doubt.