My perspective is that of a person that focuses on the business side and no longer programs but has in the past:
The thing you do in entrepreneurship is essentially 'solve problems' day in and day out. You are constantly resource constrained so you must figure out how to maximize efficiency , whatever that may be in each respective case.
You have an idea (let's assume it is a good one for simplicities sake) but lack the ability to implement. This naturally brings up the question of how to implement - you can learn to do it yourself or hire someone to do it for you. Hire may mean trading equity for the "co-founder's" time or compensating them monetarily. If you cannot afford to hire (try elance, guru, etc) you are left with trading equity. This means that you must now convince someone that you are competent to direct the implementation process ("you bring something to the table").
This is meant to be a pretty straightforward explanation because your question is vague in the sense that the situation you allude to has multitudes of variables.