A tab does not mean 8 spaces. That's the whole problem, people keep thinking tabs and spaces have an exchange rate.
If you have a source file with only tabs (and you should, then nobody has to run an re-indent script because they can't read it), you should be inserting tabs. If you have a source file with only spaces, you should map the tab key to insert the correct amount of spaces before editing. If you have a source file with both tabs and spaces for indentation, you should re-indent.
Type this in a bash terminal: $ printf '1234567890\n\tx\n'
For the second paragraph: I couldn't agree more. There's even some "geniuses" that indent python with the 1st level being 4 spaces and the second level as a tab. * sigh *. Really.
If you have a source file with only tabs (and you should, then nobody has to run an re-indent script because they can't read it), you should be inserting tabs. If you have a source file with only spaces, you should map the tab key to insert the correct amount of spaces before editing. If you have a source file with both tabs and spaces for indentation, you should re-indent.