The shortest description of Y Combinator I can think of is a "Venture Expediter"
The point is, YC is really smart money in real small amounts. If you need more money or don't need so much smarts behind it, you go elsewhere on the funding spectrum.
More generally our goal is to get startups closer to later stage investors, whether angels or VCs. Pretty near 100% of startups are looking for at least some additional investment.