[...] In short, 8-char indents make things easier to read, and have the added benefit of warning you when you're nesting your functions too deep. [...]

Taken from Linux documentation (Doc*/CodingStyle) Chapter 1.

I think this explains very well the idea behind the 8-chars tabs "movement".

There are heretic movements that try to make indentations 4 (or even 2!) characters deep, and that is akin to trying to define the value of PI to be 3.

(The second quotation was just for fun :D)