Pros
You get to be a part of the mission that the customer performs.
Cons
(From my experience at TASC...) When there is a government shutdown, employees don't get paid. They either have to charge against their Paid Time Off (which is like taking money out of your own pocket) or you don't get paid. Unlike the government, no real attempt is made to get the customer to provide back pay for the time that employees are locked out because of a shutdown. The company also makes no allowance for the financial losses that employees experience. There is no reimbursement for the forced time off. The executives still get their bonuses. The owners still get their dividends. But the employees take it out of hide. Employees don't take priority. If a project manager is faced with a choice to furlough employees to make a better impression on a junior grade COTR or stand up for their employees, the employees get furloughed.