Google AdSense advertisement on your site represents an opportunity to earn some significant money that will defray your costs and even provide you with an additional source of income. When I established this blog, I deliberately decided not to include any advertisements because I wanted to make it clear that I was not motivated by potential earnings.
When I registered for Movember I decided to temporarily enable Google AdSense ads for the month. I was partly hoping that this would provide me another way to collect money for the charity, but I was also experimenting to see how much money could be earned from this stream.
The bad news for the Irish Cancer Society is that this did not result in a significant revenue stream. In total I earned 7 euro and 64 cents during the month. Since they don't allow you to withdraw any money until your account earnings exceeds 10 euro, there was very little chance that I would consider giving up my day job and living off my AdSense earnings (in order to ensure that the charity didn't suffer I made a personal donation in lieu).
This experience, matches the experience I had a few years ago with trying AdSense advertisements on the web site of a local soccer team. The earnings from google were negligible, while the club had no problem convincing local businesses to pay several hundred euro per year to have their logo appearing on the web site. Of course, it could be the case that the local businesses are paying above the market rates for the existing advertisements - in fact many of them may be consciously doing this in order to build up good will in the community or to support what they believe is a good cause.