Unequivocally, yes.

You can haggle over the $'s and %'s all day - but what you can't argue over is where your company stands after YC, especially in the eyes of customers & investors.

Some people have the ability to never worry about investors, but for those who don't, it is insanely helpful. And most of the shift in opinion is based on how your product is being used by customers, which is the primary focus of many YC partners.

Once again for good measure: Yes.