One important thing about keyboard is that it is a mostly uninterrupted buffered stream: with some notable exceptions, you can usually keep typing whether the previous command is done executing or not. You can type ahead several long running commands (in a shell, in an editor, for instance) and then let go. Or, you can click, wait, click, wait, click and then finally switch to something else.

Is it a big deal? I suppose it depends on how much you think in terms of whole sequences of commands.