With no downsides to using tabs over spaces, and wanting to preserve readable SCM diffs, saving 20% of the space for such diffs just happens to be a nice side b

With no downsides to using tabs over spaces, and wanting to preserve readable SCM diffs, saving 20% of the space for such diffs just happens to be a nice side benefit, not the primary one. (The primary one being flexibility in presentation.) Saying you don't conform to a use case does not invalidate said use case.