Most of the time when there's no client, you get to hang out and chat. For private events, the event overseer usually includes a house tip which you get to split between the valets. A lot of down time where you get paid for standing around.
Cons
You have to travel to the location that you're working for a private event. And, you don't get paid for time on the road as you commute there. Plus, gas doesn't get reimbursed.