it's not always 'hungry' so much as natural reaction to something catchable in the vicinity.
there is a concept in aquaculture called assimilation efficiency, which is a measure of materials physiologically captured via digestion compared to what is ingested. Actually, it is easier to measure what is offered vs what is excreted in experiments. Anyway, the point is, whatever an animal eats does not equate to what is incorporated and used in their bodies. People can drink two glasses of orange juice a day but our bodies will only use so much vitamin C... we just pee out the rest. So there is merit to reducing your feedings... you're just putting it in the coral so your coral spits it out in a less digested state... and your water quality is reduced.
Additionally, (speculation only), I wonder if frequent feedings have any impact on whether a coral is more prone to expel their zooxanthellae. The reason for this suspicion is that as nitrogenous wastes are produced for their algal endosymbionts, they have to regulate their level (density) of zooxanthellae for optimal light capture efficiency, carbohydrate production, and zooxanthellae waste levels (oxygen toxicity?). Additionally, there's some indication that corals will first 'prefer' zooplankton captured energy followed secondarily by zooxanthellae photosynthates. Reference abstract here:
http://scholarspace.manoa.hawaii.edu/handle/10125/2241