The Northern California Fly Fishing Board

It depends on the water. For skinny water use a tiny indicator. For heavy/fast water use one of those big Bole's yarn indicators they sell in the fly shop.
Personally I find I catch more fish when I can high-stick without one and only put one on when I'm fishing big water. On the other hand Bjorn will catch just as many, or more, fish high sticking with an indicator on. It all comes down to how you feel most connected to your flies.
Don't let others tell you how to fish. Find out what works for you and don't be concerned with people's labels.