Why do you need to maintain control? Greed? Paranoia? The idea is too complex for others to understand? (note: none of these are good reasons ;) )
As a leader, you should always strive to ensure that you can be replaced, and that the company can and would continue without you. This is often a big hurdle for many entrepreneurs to wrap their head around, but it is almost always critical to the success of the company.
In the beginning, the founders maintain full control simply because they are the only ones that fully understand the idea and market. Over time, you need to do less innovation, and more operation of the business. Founders rarely make good full-time CEOs, and "professional CEOs" rarely make good founders, but they both play their part in the on-going success of the company.