I don't want to commit temporary debug cruft to version control, so I'd still need to keep adding and removing that whenever I do a commit. Though I guess I could just always skip it with git add --patch.
I do have need for some solution, since I have packages that don't do anything with strings and therefore don't import fmt, but which still get bugs which I need to debug with the stdout.
One more robust approach would be to fit a complete configurable logging system permanently in place.
That way it will never complain that fmt is imported but not used.
Still, I never had need for this. Once you have written a bit of code the import list remains relatively stable.