Did you ever notice that the most successful bloggers all have unique blogs? More importantly they all choose blogs that fit the topic of their blog and don't overly distract you from the main purpose of their blog.
Here's the problem with most blogs The blogger simply chooses the wrong theme and this hurts them because it conveys a poor image to the reader.
If you choose a poor design and color combination that doesn't seem to fit your blog content.
You may be losing out on tons of profits.
Let me explain the format of your blog may cause visitors to leave your site without taking any of the desired actions that you choose, if your site is not formatted in a way that draws visitors to your desired action you will not make nearly as much money despite what you may have learned, this is true, the most successful bloggers have continually optimized there blog to make them the most amount of money, it is not a by accident these bloggers have pleasing and inviting themes and blog style formats.
Listen, even the color combinations you choose cause your visitor to feel a certain way.
If that feeling coincides with what you want your visitor to do you will make money, if it doesn't then you blog visitors will simply leave your site without taking any of the desired actions that you choose.
Do you think it is important to choose a good theme that compliments your desired action and as a result makes you more money? Or would you rather continue using those poorly formatted and uninviting free themes that you are using?