Pros
Good place to gain experience and quickly advance from entry level. You will be given the opportunity to learn a lot and really hone your skills working with clients. Flexible schedule/ability to work from home once you have been there about a year. (Must first "prove" yourself.) You can take time off for appointments in the middle of the day, leave early to get the kids off the bus, work from home for repairs, etc. Opportunity to learn about a variety of industries due to working on multiple client projects. Wonderful people at the entry/junior/mid-manager levels who will invest time in you to help you learn company processes. Fast-paced work environment where you will do a lot of different things everyday, so it never feels like you are operating on repeat.
Cons
Once you have become a Senior PM (usually takes about 3-4 years), there is not much room to grow or increase your pay unless you are willing to wait 5-10 years to reach the "VP" level. Expect to be treated like a number, without the opportunity for differentiation or recognition, even if you make a compelling case for yourself. Your only opportunity to get a noticeable pay raise will be through promotions, which you will eventually top out on as noted above. Senior management has little interest in providing support to solve problems that could improve the business and resolve internal inefficiencies that actually impact clients. If you identify an issue and viable solution, prepare to be shot down if it requires any monetary/managerial/resource support or a tough conversation. Very reactive, slow to change, and conservative management that operates in a spreadsheet rather than a real world business. It seems management is more interested in maintaing the status quo internally and externally than actually improving things, as referenced above. Executives will say that the company has a wonderful culture, but nearly every employee beneath the Senior Vice President level is miserable and has almost no respect for senior management. Pretty high turnover - Company will tout that there is great average tenure among employees, but in reality there are ~25 people who heavily skew that statistic. Turnover is very common within 2-4 years for junior level employees, which can make project staffing and transitions a nightmare.