I think its a good idea for any fish. It reduces the possibility of overfeeding and, related to that, it reduces the amount of waste (both fish waste and decaying food) in the tank. I find it also makes my fish scavenge for food a little more.
I think in my case it's beneficial. I've got 4 female bettas in my community 55g. Total piglets when I feed the tank. Probably fine for a lone betta as well.
i will fast my fish for several days at a time (2-3 days)because i feed 2 much. and during that time i usually will do a couple water changes during those days. the only tank that i dont fast is my 2 10 gallons because i only have bettas in there.*at least for now *
Fasting fish once a week is a good idea especially if you feed flake or pellet food. This sometimes takes longer for them to digest and they'll just keep eating. Giving them a day to clear out their digestive system will help keep them healthy.
The only fish I do not fast one day a week are the ones I'm conditioning to breed. And they mostly get frozen foods so there is less chance of digestive clogging.
thanks for all your answers. I appreciate it. My betta is situated right next to me when I am at the computer and he is always asking for food. I don't feed him much anyway, but now will definitely fast all the fish one day a week.