What are they and what you can expect from them.

First of all are individuals (or companies) that have connections inside sweatshops. Having these connections is not a bad thing, you can be sure your resume will get in front of the person directly interested in hiring you, you can be sure (not always) that your resume will be a little bit more special - will in front of the "line".

I think these are the only pluses for a head hunting companies. OK, I can remember another one: if you are new to job market, or you changed trades, or you are a fresh immigrant, than you can use the head hunting companies to find out if your resume is good, if you have chances on the job market (it is not bad and I would recommend to try this approach).

Now the bad parts of head hunting companies:
- for them the client is the hiring company, you are nothing in front of a head hunter, the head hunter will try to use you or for a job that nobody wants - jobs that are real but you can see them posted for months and months even if it is recession, jobs really bad paid but with requirements equivalent for a space engineer and as I said before, if you fail that interview the HH will not answer your calls or emails for him you are a "failure". To be sincere I consider these kind of head hunters some im*****es, rude individuals with brains the size of a peanut.
- Another way of not being your representative, but the representative of a sweatshop....