As one who forges about 95% of everything..... it's rare that I start with anything less than 1/4". I'm a big believer in distal tapers, which means that I can take a pretty small piece of 1/4" stock, and turn it into something.
Personally, I don't think it's about the thickness that one starts with.....but what you do with it in terms of geometry and heat treat to fit whatever the thickness is. In terms of grinding/finishing, I live by...... "I can always remove material if I want/it's needed....but if it's too thin, I can never put any material back." That means I ALWAYS start thick, and if necessary, make it thinner.