I believe Leapordsknowbest is referring to the old style fist (aka shuri fist) in which the index finger is pressed against the palm with the thumb pressed against it (see Victor Smith's article on this site).
I use it as my primary fist. It is the standard fist formation taught in Shuri Ryu. I personally prefer it for the majority of fist techniques. However, I, like most decently experienced karate-ka, have a tendency to switch between fist formations i.e. regular and verticle, for certain techniques.