It really isn't. As another user said below, following long function call chains is counter-productive and if you don't have an ultra strict function naming policy you will have functions with duplicate functionalities very quickly.
> following long function call chains is counter-productive
Well, be productive then!
It is a heuristic. I don't think I am in the minority saying that "breaking things down in small manageable chunks is a good thing". That's is not just Erlang that's common sense. That's the point. That doesn't mean having to count lines if you go over 7 start making functions like next1 next2 and so on. That's called being pedantic.
Breaking things down in smaller easier to understand pieces if you can applies to any language probably. 7 lines is just a heuristic.