Pros
Depending on what department or division you end up in, the pay can be good and the jobs tend to be relatively stable. Some departments and divisions exude positivity. Those are the best.
Cons
They do little to develop management’s leadership skills so you may end up with a horrible manager through no fault of your own. Problem managers or supervisors do not get adequate coaching. Some nurture their employees and others actively try to ruin those they dislike. There is an undercurrent of discrimination in some divisions, as another commenter noted. It is easy get stuck in the same job unless you jump from one department to the next. The County likes to do things the same way they have always done them. In more than one department, I noticed the smartest new employees tended to get pushed out or leave. There is a reason for this. If you find yourself in a division with a bad manager, get out as soon as you can.