My users frequently use Shift+Tab to unindent [Outdent] code.
We have found that it only works so long as the cursor is not at the left margin.
For example, if the line starts with 4 tabs and the cursor is after the first tab they are only able to use Shift+Tab once.
After that it has no effect.
They want to be able to use it 4 times in this case - to bring the text to the left margin.
Other editors [including the one I used to use in my product] ignore the position of the cursor and allow all 'prefix' tabs to be removed no matter where the cursor is positioned.