What does they do exactly and is there any money in it?

They do own most of the means of production (TV studios, etc) or do they act more as middlemen?

Anybody got experience with them? It seems to me a lot of them are using an awful few personnel for the $$$ they rake in(at least in my city).

I have done some contract writing for M&C Saatchi in a past life and it's a mix of insourcing and outsourcing. Generally "creatives," writers and designers are on staff but a lot of the TV and new media production will be outsourced to third parties. The main goal of an ad agency is to completely take care of the marketing needs of their clients - ie. they will completely plan, design and implement all of the marketing campaigns for their clients, including transparently liasing with and managing outsourcers. The client makes the product and then the ad agency has the task of getting people in the door.

I saw tons and tons of waste in mainstream / offline advertising. That shit wouldn't fly for a second compared to results based online advertising companies where every single click is costed and quantified. Tons of "cool" ideas that were obviously not robustly tested, but everyone stood around congratulating each other about how brilliant and stylish they were.

If you watch the TV show "Mad Men" then that is actually a pretty good picture of how many ad agencies work, including the schmoozing, bullshitting and expensive company lunches.

Most of the established ad companies have got all resources of their own but some do outsource also.