That is good. However I'm still not clear on whether people like me, who already have an `fsaverage` in their `subjects_dir` (which I imagine is most folks) would absolutely need to or just want to run this function for best functionality (what would be the drawback without doing it?). I assume it's necessary, in which case it might be good to list the necessary files so users can copy them themselves manually if they want. Consider if a user already had an `fsaverage` with lots of other useful data in it, it would be a bummer to have to figure out what to copy and what not to.

Maybe an `overwrite` option would be good that would just copy the `mne` files over if `fsaverage` already exists...