If you already spend a fair amount of time blogging, money may come to you literally as soon as you ask for it. Once you have an established blog with a regular readership, it is easy to turn a profit through advertising.
By hosting sponsored links or banners on your blog to monetise it, you can see income from your hobby almost overnight. Even if you did not start your blog intending to turn a profit, making supplementary income from your blog is easier than you think.
For people who have spent months or years blogging, money from advertising revenue may still not add up to a large sum. The amount of money that you can make as a blogger depends on a lot of different factors, but perhaps the most important element of the equation is the topic of your blog.
If your blog is on a subject that appeals to a demographic that advertisers have a strong desire to reach, you will be more likely to be able to turn a large profit on your blog than if your blog is on a fairly obscure subject that does not draw the kind of audience that advertisers need to appeal to. The only way to find out where you fall on this spectrum is to try hosting some ads.
If you are already blogging, you have nothing to lose.