Per the Linux kernel coding style document:

The answer to that is that if you need more than 3 levels of indentation, you're screwed anyway, and should fix your program.

What can I deduce from this quote? On top of the fact that too long methods are hard to maintain, are they hard or impossible to optimize for the compiler?

I don't really understand if this quote encourages better coding practice or is really a mathematical / algorithmic sort of truth.

I also read in some C++ optimizing guide that "dividing up a program into more functions improves its design" is frequently taught in CS courses, but it should be not done too much, since it can turn into a lot of JMP calls (even if the compiler can inline some methods by itself).