Some years ago I've downloaded the ebook "C++ Manuale di Stile" (C++ Style Manual) written by Carlo Pescio and in these days I'm reading (again) some of its chapters. One of them is devoted to tabs:
[...] in a big project in which I participated, "the length of the tab" was cause of severe tensions, with threats of layoffs and endless discussions. Even in this case, the basic problem was the lack of a standard accepted by all: some programmers defined the tab as eight spaces, other two, other three. In addition, some used only tabs, others used both tabs and spaces.
[...] it's necessary that an internal convention is established and it's respected by every developer. It's better to resolve disputes at the beginning of a project than being in the middle of a civil war when development is in progress.
From pages 56 and 57 - Translation by me
I've already written about the need of a common coding style but, as ancient Romans used to say, repetita juvant.