The main claims of garlic is 1: stops ich, 2: boosts appetite
If you read through the threads on ich, you will see some reccommend feeding garlic to cure ich while others disagree. If I can throw my 2 cents on the topic, I look at garlic like we look at the herpes medications we all laugh at on TV. It doesn't cure anything, it just helps prevent outbreaks.
That's why you'll see some people have good results while feeding garlic, but once they stop, ich seems to reappear.
As far as the appetite thing goes, my fish are chubby b1tches anyway and in my experience, I haven't noticed any difference between feeding with garlic and not.
Garlic is a terrestrial vegetable which kind of goes against the grain of being an "appropriate" fish food, but I look at the benefits it has in our diets as far as healthy hearts and reduced cholesterol. I've used the bottle form as well as the chopping method.
The key is to keep your fish eating to keep them healthy. A fish that is not well fed will have a weaker immune system. Once a fish stops eating, in most cases the fish is a goner. If you feel they eat more with garlic in their diet, keep going.