Pros
Opportunity for international postings, and exposure to large scale enterprise. The experiences you gain while working there, though they may not feel that great, will be very useful at other jobs. They have a laser-like focus on cost-cutting, which will stay with you in successive roles, even if you chose not to act on the instinct.
Cons
Money is truly the only thing that matters at SGS; quality, safety and professionalism are only ever considered as an afterthought. There are good people working for the company, but most of the ranks are filled with those who are either not in the position to move to another company, or afraid to. The pay is low for most, and the company response to fixing any problem is always to say that the problem doesn't exist.