Vantaggi
The company is stable and is in no danger of vanishing. Layoffs are minimal and there are amazing people with a vast amount of knowledge to work with, and all are happy to help out where you may be lacking in procedure, law, or best practice.
Svantaggi
If you accept a job negotiate your salary like crazy!! What you start at will most likely be pretty close to what you end at. Unless you are in payroll - there isn't a lot of opportunity to move or advance. Most of the management has been here for 20+ years and they aren't going anywhere any time soon. If you do AMAZING on your yearly evaluation, you get about 3%. If you do average on your yearly review you will get about 3%. If you are lower than that, you'll probably get an improvement plan, or fired. ADP has wonderful people - but they are extremely tight-fisted. Everything is on a scale. Instead of giving local management the power to promote and reward their people, it's all based on scales.