Re: Usability suggestion : completion for M-:

[Richard Stallman]

    For what it's worth, I'm a bit annoyed by Emacs's inconsistent use of
    TAB: in minibuffers, TAB behaves like in terminals to mean "complete",
    where in normal buffers it usually means "indent".

There aren't enough convenient keys, so we have to do this overloading.

    But of course, "indent" can also make sense in minibuffers,

It can make sense, but it is not very useful in minibuffers.  We
wouldn't recommend writing nontrivial Lisp code in a minibuffer, for
instance.

    "complete" also makes a lot of sense in normal buffers.

Yes, so we use M-TAB for that.

It isn't perfectly elegant, but I think it is the best solution
available given the constraints of the keyboard.

    I have used for many years commands that do both bound to TAB: typically
    my TAB first tries to indent, and if the indentation code didn't make any
    change then TAB tries to complete.

I think that would be unpredictable and therefore inconvenient.