By itself, it should not be a useless tag: some questions are about configuring emacs, other are about using emacs.
Even if we exclude questions about a specific configuration area, which could and should be tagged accordingly, remain some general configuration questions.
Most of these general questions could replace configuration with the much discussed init-file tag.
So the only usage of configuration that I can think of would be to make a difference between "configuration" questions, and "usage" questions (together with additional tags). Note that this distinction is itself a very thin line: most "usage" questions end up involving some variable to set or some defun to evaluate, and it is usually trivial to adapt such a "usage" answer into a "configuration" one, by adding the relevant bit of elisp to the init file.
So... yes, in my opinion, we don't really need that tag.