There is a timeout on multi-key mappings, so if you need to type fd0 you type f, wait 'timeoutlen' (1 second by default apparently), then type d0.
That's a pain, but it doesn't come up often. In return you get quite a lot of functionality (due to vim being modal) without having to move your fingers beyond the letter keys, which is quite relaxing.
What if you need to type "fd" in insert mode? Like fd0, fd1, etc. Isn't that going to be a pain? Do you never have to type "fd"?