Difference between Action() and RenderAction()?

In asp.net mvc2, what's the difference between

Html.A开发者_JS百科ction(...)

and

Html.RenderAction(...)

?

Phil Haack does a great job explaining the two methods in this post.

"The difference between the two is that Html.RenderAction will render the result directly to the Response (which is more efficient if the action returns a large amount of HTML) whereas Html.Action returns a string with the result."