Ask HN: How do startups manage their systems, policy and procedures?

What do companies like Google, Microsoft or Apple do to manage their systems ?

There is alot of talk about the methods to improve systems like Theory of constraint, Six sigma and lean thinking, how does that goes into all of this systems approach and managing them from a startup perspective ? According to the book E-Myth by Michael Gerber and The Goal by Eliyahu Goldratt; these folks advocate systems thinking and creating systems in your company.

But what if I'm a small startup with 10-20 employees, do I really need systems ? What if nobody cares about these documents and just do what they think is worth doing according to them ? And how do these systems/documents will help me in case of some disaster e.g. marketing failure or no revenue from products ? How do I get most out of these systems ?