they exist purely to make money and are basically taking advantage of the disorganised mess that society is in. few of them can really appreciate your skills and I've never had an accurate description from any of them for the job I was going to do, the job I'm doing now sounded more like the store man than the quality inspector when they explained it. luckily i had already worked for the company a few months earlier and as soon as I went to talk to them and they told me who i was replacing i knew what it was about.
The costs they charge companies are also ludocrous, few agency workers are given more than the national minimum wage and in the UK thats starvation pay not even enough to pay rent with - oh but then you can't rent a house these days in the UK if you are an agency worker, the world of work goes through agencies but working for an agency counts as being practically unemployed if your trying to do something that involves financial comitment your at a loose end, no loans, no mortage and no renting a house.
the only reason why I fitted well into my current job was because I knew the company already and the company knew me and what I could do and decided to give me a chance, they rang the agency and asked for me specificly, otherwise I'd still be on and agency in a warehouse packing stuff.