Pros
It can be flexible if you are highly utilized because your client is really your boss, so you can work early or late depending on your clients needs. Large pool of resources to staff your projects with around the world and in many different areas of expertise.
Cons
Management for my entity, CES, was poor at the local and national office. Growth potential in the company is very low. I was performing way beyond my level of pay and the management was not smart enough to charge clients more for the services they were receiving or pay me for them. There is no team environment. Everyone is always out to charge as much as they can for work and don't look to share work when they have the opportunity. The quality of work from most team members was really low and a liability to the Project Manager and Company.