Nowadays there's a trend for clients to (partly) make their own advertising. Some clients hire creatives to directly work for them. And some clients save costs by doing certain things in-house. Advertisers nowadays even talk about that this might be the 'future of advertising'.
One client at our agency executes their radiocommercials itself. We just need to write them and they do the rest. Yesterday I worked for a client who made a photograph itself. The photograph was horrible, even though it was made by a professional photographer. It was totally worthless to an extend that even the best Photoshop couldn't save it anymore.
One of my teachers from a concept course used to say "imagination is a muscle". Just like muscles, you need to keep on training your imagination. This means that a client, who makes creative work on the side can never be as good as an agency that is constantly busy making creative stuff. A creative cell that works directly within a company, that could work. But only if you hire top creatives who get the chance to work without interruption on creative assignments and get total freedom to make quality work. Google is a good example of a company understands what creativity is about. Almost all of the others will be better off to leave the creativity to the experts.
Well, history is repeating itself. About 10 years ago advertisers also thought they could do their own advertising. Most of these 'pioneers' of in-house advertising now hired an agency again.