Though I agree that there's a reductionist aspect to this declutter thinking, I've always thought the answer to this question is "an ordered mind", which is very different from an empty mind of course.
I think the implication was "an empty mind." Picture not a cleared-off tabletop, but an office desk with drawers where both the desktop and the drawers are empty.
“If a cluttered desk is a sign of a cluttered mind, of what, then, is an empty desk a sign?” – Albert Einstein