Because sometimes you must use spaces, because you are indenting a continuation line that should be indented to an exact spot with respect to the previous line

Because sometimes you must use spaces, because you are indenting a continuation line that should be indented to an exact spot with respect to the previous line (you're in the middle of an expression, you want to be at the start of an open parenthesis, etc). Surely the suggestion in that case is not to carefully insert tab characters to the same indentation of the previous line, and then spaces for the rest, so that you have some tabs and some spaces on the continued line? Anything else fails if the tabs are set as "developer preference" on display, but that tabs + spaces on one line is incredibly fiddly.