Pros
The best reason to work for KPMG is the opportunity to work on a variety of clients that would only be open to someone associated with one of the Big Four accounting firms. The career path is fairly straightforward (as compared to working in industry), and if you stay the course and focus on your own development there is always room for advancement. This is due to the fact that so many people leave for other opportunities at various levels. For the most part, the people you work with are also very talented so you can learn a lot from them.
Cons
Depending on what project you are working on and the time of year the work/life balance issue will always be the number one reason people decide to leave KPMG. It can vary from manageable to downright unbearable. At its worst you may find yourself staffed on multiple projects at the same time working for different managers/partners who all have competing expectations and no coordination at all. It falls on the staff to make the tough judgment calls and personal sacrifices to get the work done. The reason it works is because typically the staff are hardworking but at some point everyone feels burned out.