G&F stocks them in Greers (and other lakes) to control Gizzard Shad, which can become overabundant without large open water predators. Stomach content analysis indicates that they feed mostly on shad and very seldom on game fish. I know there is a big difference of opinion on this issue, but most studies seem to indicate they do not do harm to other popular game fish.
They are naturally sterile (as are many hybrid fish) so must be restocked frequently.

I too enjoy catching them and they can be fun and exciting top water action at times. But to each his own