The point of the "tab" option is that there is no consensus on the number of spaces to use -- so by using tab, one uses a single character, and allows the developer to determine screen spacing to their comfort. "Tab" being a live option is a symptom of the war-never-over in absolute spacing degree -- since different people have different eye-sight, eye-strain, etc. constraints, different linguistic familiarities, cod…
The war is ending though. It will be over when we finally format code at read-time so that we respect the viewer's preferences, instead of at save-time to reflect the authors'.
Read-time revisions to spacing need, only, to change the non-intentional elements of spacing -- indent depth is a very good candidate for this (hence the tab character!).