It has worked for me aswell and I still always carry treats with me to reward for a particularly good performance (in the face of a huge and unexpected distraction, for example). Having said that, I'm sure it can be trained just as well without but a lot depends on the particular dog, some dogs don't lay much value on food (so they tell me
), but if used correctly as a tool, as opposed to a prop, then I don't think they're a problem. If "good boy" is associated with something yummy, then eventually "good boy" will be reward enough in its own right (same as the clicker), but from a dog's point of view, "good boy" on its own is not exactly a motivator. I do think its a personal choice though, there's no wrong or right way and I'm sure there will be lots of people here who train successfully without.