It is decent information for most community tanks, since you don't want to have a bunch of food left afterwards that sits on the bottom and rots. I don't think there is a single tank that should be fed "what the fish can eat in a few minutes"... they'll just eat too much. The problem is that bettas are pigs, and will eat way too much in a few moments, if you let them. If you put in 10 pellets, a single betta can eat that in well under a minute, and it's not good for them.