This used to be long an complicated. With all manner of comparisons and discussion.
But I've decoded to cut it down just to essentials and keep it very short and equally sweet.
Since working on a PHP codebase with an in-house style-guide that specifies TAB, I've come across this little frustration that drives me a mad every single day.
Let's say you've got a REPL or two in your development environment. There's a strong possibility that that REPL will use TAB completion.
And now imagine you need to cut and paste code from your editor into that REPL to try things out... that's what REPLs are for, right? You cut the code from your editor and your REPL tries to TAB-complete each and every start of line and throws a fit.
So you need to cut and paste your code from one editor into another editor that still permits space indenting, edit all the code indenting, and then, finally, you get to paste it into your REPL.