If you make it into YC you are a part of basically the most well connected network in the tech and startup world. You are put on a mailing list with literal billionaires (including Chesky from this post) and you can talk to thousands of startup founders for advice or connections. It's also insanely valuable because if you have a new tech product your fellow YC founders can use your service and that gives you a large base to go off and people giving you advice right off the bat.

In any case, getting into YC is literally equivelant, even much more prestigious in some ways than going to Harvard in terms of what it means on a resume. You arent ever going to have trouble getting a job if you have YC on your resume.

YC was the first startup accelerator/incubator to the best of my knowledge. This might not be true anymore but as of about a year ago there were only 11 or so startups in incubators that attained "unicorn" (billion dollar valuation) status. All 11 of them went through YC. For reference, there are now 2500 incubators on earth. YC is absurdly valuable.