What's YC's role in companies post demo day?

"Though YC continues after the 3 month cycle, and the alumni network is an increasingly valuable resource, those 11 weeks are still the most important thing"

I'm sure the answer varies company to company, but I'm curious what role Y Combinator plays in companies after their respective cycle? Through YC/HN, there's definately some support for the ongoing needs of graduate companies-- such as hiring (https://news.ycombinator.com/jobs) and alumni networking.

Specifically, does YC provide any support for later stage activities such as additional funding rounds, M&A activities, or operational expansion? With the number of YC companies whom have gone on to successfully execute these later stage activities, it seems like there is some sort of support structure in place for these companies post graduation. Does YC even want to be involved in these later stage activities? I could see the benefit in staying somewhat 'hands off' and just focusing on the core 11 week startup cycle. Anyone with any experience or insight?