Pros
The big obvious benefit is getting to work on what you hope will be a breakthrough technology. It's great to be able to work in an environment where you get to think about this new fundamental way of interacting with the future of computing.
Cons
It's a very toxic work environment that feels very cargo cultish. Making actual progress towards business goals isn't as important as seeming like you've "bought in" by appearing to work really long hours. Having specific suggestions for how to improve things is met with ridicule as implementing them would mean having to admit that things weren't working. An excess of meetings, managers and competing fiefdoms with long hours and very little actual work getting done. As a startup you might expect for things to be dynamic and quick paced, but even the littlest decision must be ratified and approved by a stack of people. I've worked with Fortune 1000 companies that executed faster. The frequent strategy changes result in much of the work you do getting tossed aside. This is very demoralizing when it's the thing you've been killing yourself to complete for weeks as it was very urgent up until the point it was deemed unnecessary.