Pros
Flexible schedules (provided you "make up" the time whether it be late at night or on the weekends); encouraged and if merited, compensated cross-selling between agencies and practice groups; ability to work on projects outside of your expertise area if you are a hand-raiser.
Cons
Corrupt practice heads who play favorites and talk behind their employees' backs; zero transparency during the merger between inVentiv Health and INC and even less when going public as Syneos; insane focus on billable hours; employees vindicated for taking sick days, which by company policy, are 'unlimited; angry and overworked practice heads and managers make for a very tired practice group who do not know how to help but only to be yelled at and scramble to figure things out; favorites played amongst who gets to go on new business pitches....the list goes on. If you are >5 in to your career you can do well here but don't expect to excel as a senior leader. Oh and, compensation is absolute rubbish compared to other agencies. Bonuses are tied to the overall PR group so if one practice is not high performing, you bear the brunt personally.