As a pro, methinks "everything needs to get done" is the main one. It's a trait shared with all small companies, and can be petty things like buying the coffee to coming up with a plan to do X and overseeing it because nobody else has time. If you're able to take initiatives the startup/SME world is for you.
The main con in my personal experience is the grueling entitlement of some founders. Not saying this applies to any or all YC startups (never worked for one) but there are founders out there who expect an arm and a leg and then some, fully expecting their employees will work long hours for peanuts. I'm assuming this is less of a problem at YC companies since they seem reasonably well funded and able to actually pay employees properly (if not you're doing a good job at PR but shame on you), but it's worth raising if only in passing.
Another big con IMO is lack of experience of quite a few founders. The best way to frame this might be a lack of insights in the industry they're targeting. Rewarding turning a business model into something that can work with a pittance of cash and equity is not very enticing to say the least. I've seen this play out from within and without and it's just plain ugly to see whoever came up with the bright idea being thrown a bone as means of thanks while the founders and their VCs laugh on their way to the bank. With respect to this, methinks try to teach humility to founders you work with: if an employee or a consultant shows a much better way then by all means invite that person to the team as a cofounder or nearly so. It doesn't matter if there has been 3 or 5 years of work poured into a hopeless idea before that. I've seen more than a few startups where someone put a brilliant improvement forward only to be shown a bone as a reward, finding a new job as a result, and the startup eventually going nowhere or failing from lack of execution.
The main con in my personal experience is the grueling entitlement of some founders. Not saying this applies to any or all YC startups (never worked for one) but there are founders out there who expect an arm and a leg and then some, fully expecting their employees will work long hours for peanuts. I'm assuming this is less of a problem at YC companies since they seem reasonably well funded and able to actually pay employees properly (if not you're doing a good job at PR but shame on you), but it's worth raising if only in passing.
Another big con IMO is lack of experience of quite a few founders. The best way to frame this might be a lack of insights in the industry they're targeting. Rewarding turning a business model into something that can work with a pittance of cash and equity is not very enticing to say the least. I've seen this play out from within and without and it's just plain ugly to see whoever came up with the bright idea being thrown a bone as means of thanks while the founders and their VCs laugh on their way to the bank. With respect to this, methinks try to teach humility to founders you work with: if an employee or a consultant shows a much better way then by all means invite that person to the team as a cofounder or nearly so. It doesn't matter if there has been 3 or 5 years of work poured into a hopeless idea before that. I've seen more than a few startups where someone put a brilliant improvement forward only to be shown a bone as a reward, finding a new job as a result, and the startup eventually going nowhere or failing from lack of execution.