Vantaggi
There are definitely good opportunities for growth depending on which area of the organization you work in. I worked in a small field office with a great boss for Gallagher Benefit Services and mostly had a good experience. You get an opportunity to work with a lot of different people and that's very helpful for career and personal growth. Benefits were ok - not great - with the exception of the 401(k) plan because they have an awesome match.
Svantaggi
Ivory tower headquarters sometimes would dictate incredibly unworkable and stupid plans to the field offices. There are good people in the organization and there are also some incredibly lame ones. Never fun when the lame ones are in a position of authority and make really stupid decisions that impact everyone!! One thing that bothered me was how willing Gallagher was to screw the employees if it meant pleasing the shareholders. (I imagine it's the same for all the large corporations?) When the economy tanked a few years back they stopped giving raises and they froze all holiday parties. The economy started recovering, stock prices started rising and then they still wouldn't give raises or let you have holiday parties. I can't tell you the # of lame "explanations" I heard from corporate leadership. They pushed as hard as they could without wanting to give back. With all that said, I don't regret the 10 years I spent there. But I'm very glad to be at a smaller company now that values employees much more than Gallagher did.