One of the (I thought) most useless courses I took in B-School was called Organizational Design - it seemed mostly to be about whether to put functional hierarchy or geographical hierarchy at the top level of the company. At some point during my startup experience I realized that OD is actually important, but the key insight is that it isn't a static thing - a single chart that you make and that's it. Instead it's dynamic, changing as the company grows, and as the people within the company grow.

How you manage the hierarchy of a growing company is crucial to managing people. It's nice to think that at a startup everyone is egoless, and will do what needs to get done, but its not true in the long run. People have careers and goals, and they will need to see their contributions reflected by the company contributing back to their career and goals.