Yes because if you want to deindent with tabs it is just delete one character whilst spaces requires you top delete x characters where x is the number of spaces you indent by.
For "clean-fixed-width" unambiguous indent (eg, at the beginning of lines) you can make delete also delete X=indent_width spaces.
But for "dirty-width" indents, eg, after some text that can vary in size (proportional fonts or some special chars even in fixed fonts) you can't align with spaces while a tab width can be auto-adjusted to match the other line
