I think the biggest thing that contributes to bioload, both with fish and corals, is feeding. If you have a big fat fish that eats a lot in contributes to the bioload significantly. If you feed your corals then wether the food is eaten by your corals or not then it will be broken down into waste in your tank.
Corals such as sun coral that have to be fed a lot add to the bio load significantly. Your little acro frags, usually not as much.
With corals I think you'd usually have to worry about coral war fare before bio load.
At least thats my two cents.
Jon