Pros
Generally has a lot of options and is quick to fill positions. If you need to find work fast, this is a good place to start.
Cons
They will try and place you in positions they need to fill over positions you are looking for. You have to reject the trash work to get the work you are looking for. Education counts for nothing with them. They will not give you a position if you don't possess working experience even if you possess the education for that position. They will only offer you positions they need to fill because you are more valuable to them as a general laborer than a skilled worker. Once you are sent to a job, they basically forget about you. If you express the desire to leave that job and go for another they will tell you that they can't replace you at that job. There is zero job security, your personal affairs mean absolutely nothing to them. You are a product for them to sell, not a client. Their clients are the company's they staff for, you are just the product they provide. You are nothing, and you are easily replacable.