Certain fish can actually explode, as their stomic will burst open, unlike humans many fish do not get the sensation that they are "full" but simply the sensation that it tastes good.
Also over feeding can result to very poor water coditions, extra waste from your fish raises the ammonia in the tank which can lead to death, rotting food that has been un eatten can result high ammonia and then death. Not to mention if you don't want to lose your fish and your water conditions are poor than you'll have to do continious water changes and filter changes which can be lengthy and time consuming.
IMPO a simply feed whatever your fish can eat within 3 mins and nothing more and usually not more than once a day. If food is uneatten scoop out the extra remains and feed less next time.