You get into namespace issues. It's easy to give two submit buttons the same value in your application that are supposed to go to different runmodes. In a large application, you'll probably run out of good names eventually.
I always felt that HTML using the "value" param on submit buttons was a bad design choice, and I think this illustrates that problem well. This, of course, is HTML's problem, not C::A's.
"There is no shame in being self-taught, only in not trying to learn in the first place." -- Atrus, Myst: The Book of D'ni.