the only possible benefit is that it can get you a lot of experience fast
my first job was like that, 70-80 hours with no overtime for 8-9 months on this horrible project. but i went from fresh out of college to getting put in charge of all the web service development and running 3 hour meetings with the client and assigning work to other people.
i quit right before the 1 year mark and got a job somewhere else that normally required 3-5 years of experience.
i wouldn't ever want to do it again though