I’ve been using Vim for a while now, and it’s struck me as odd that an editor with such a focus on reducing keystrokes would leave a large, easily-reachable key such as Tab unbound.

It’s huge, it’s right under my left pinky, and it’s just sitting there. I feel a little silly even asking this question, but I feel like I’m missing something.
Is there some reason <Tab> is left without a predefined purpose in Normal and Visual modes — perhaps some backward compatibility or edge case I’m not aware of? Should I just go ahead and make use of it in my own Vim configuration without fear, or is this a bad idea?
Tab and CTRL-I are the same in Vim, and it’s used to go through the jump list (opposite is CTRL-O).
From the documentation (
:help <tab>):