What are the arguments for and against?
For: A massive network of people you can draw on that surpasses literally anything you could build yourself. A decent chunk of money.
Against: Giving up a bit of equity, but if you're precious about that you wouldn't be considering YC.
Are you "giving up a bit of equity"? I think more accurately you are pointing your front tyres towards a path of aiming for fast growth and investment. YC doesn't want 7% of a $1m arr Haskell consultancy as the endgame for your company for example. They want a shot at a 10B company. See their home page and it now gives that vibe.
So more like you are giving a large chunk of equity for a lot of investment over many years to build a unicorn, unless you fail. Which most likely you will. Based on probabilities. Fail may mean getting some $ though.
It ultimately depends.
Only if the startup idea you are raising for is worth it, which now matters more than ever as execution is going to zero.
If that doesn't bother you and you need the cash now, then in summary:
If you don't mind the risk for a small amount of equity then you might as well do it before AGI arrives.For: Access to bookface network (secret network for YC founders and mentors). Against: Depends on the terms, maybe not good if you mess up the cap table allocation.