Against: Giving up a bit of equity, but if you're precious about that you wouldn't be considering YC.

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:

   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.