Vantaggi
You will work hard at Protiviti. You will travel. You will see a lot of different companies and learn a lot. You will also be on the road all the time, never be home, work 80+ hours a week, and be burned out all the time. You will do all the hard work and management will take all the credit. If you succeed though you will be promoted, and the pay, while not commensurate with the work level for the lower levels, certainly makes up for it at the management levels.
Svantaggi
The biggest problem with Protiviti is it's office culture. It's barely a step above a frat house. The average new hire is hired based on how they fit this culture, not whether they have the experience and intelligence to succeed. One look at any of their office recruiting calendars will make this obviously - they make sure to hit all the local homecoming games and state schools, but completely ignore the good ones. I can't even tell you the number of racist and sexist comments I've heard from people. The workforce is only about 15% female, and they're usually treated with the sort of sexist attitudes that should have died decades ago. I honestly can't believe that there hasn't been a sexual harassment or discrimination lawsuit yet.