3z3k3l,
Personally, I've changed my view on this. I used to think that my ponds would only ever have BG and LMB, period...but diversity has definite advantages. It seems to me, that within reason, we can find find complementary fish and in that case diversity is good. Fish which do not complement are not necessarily good.
For example, for weed and algae control, grass carp and Tilapia complement each other very well.
For small forage, I also think fatheads, shad, and even gambusia complement each other as forage providers...maybe not so much Gambusia, but I have no choice on them.
For larger forage, BG, redear, and Tilapia seem to complement each other, especially since the Tilapia die off each winter before they can become a problem to BG fry.
Predators can be complementary also. I believe that LMB and HSB may be complimentary. Not sure yet, because I haven't had enough personal experience but it appears that HSB take the open water and LMB take the structure and shallower water each finding their own forage.
Catfish, crappie, common carp are examples of species which do not complement the above mix. Some say gizzard shad shoulkd also be in that list, but I have them and so far so good.
I've totally changed my view on fish....diversity when complementary, is a good thing, IMHO. Besides, its just more fun.