A URL channel gives you the ability to track Adsense performance for a specific domain or webpage. Once you understand what works best for your particular website, you can start by optimizing for those factors.
You can group ads by size, color or slot location on the page.
Just creating a channel by itself will not increase your revenue. The custom channel or URL channel is an important factor in understanding Adsense. Also work towards removing ads or slots that are not working on your site.
Using both does not alter your data in any ways, It is just a different perspective of your data. It will also show you many website specific information depending on how you have set up your channels.
Create URL channels for different sections of the site that you want to compare. So, Adsense channels are basically a reporting option. You can view these reports under the Performance Reports tab and then the Advanced Reports section.
As mentioned, you can have URL channels and custom channels. You can create channels for a single page or a hierarchy of pages based on the URL. Is it a particular page, or a particular ad slot or an ad of a specific size etc etc. Once you have create ad units and ads are displaying on your site, you can start grouping these various ad units into channels.
Create two custom channels, one with all ad units that appear on the top of the page and another with all ad units that appear at the bottom.
Eventually these actions should pay off and increase your revenue. If you are using Google Adsense on your blog or website, you already know how important it is to know what exactly is generating revenue.
For example: You can track all ad across a section of your website or you can group an ads in a slot across all pages.