If you are a google adsense publisher and are using channels to find out the income/revenue from different websites / ad slots then you would run out of new channel options once you have used up all the available 200 channels feature. Once you cross this default limit the adsense team will automatically upgrade your account and increase the limit to 500 Channels. Read more about Adsense Channels at Google.com
Old Rule :
With up to 200 AdSense channels, plus 200 AdSense for search channels available for each publisher, you can use channels to gain the insight you need to optimize your site’s performance. It’s easy to add, deactivate, or rename your channels, and customized reports are simple to generate.
New Rule :
We noticed that you’re using most or all of the channels in your account, so we’re happy to let you know that your AdSense account now supports 500 channels instead of 200. This change is part of a limited beta test we’re conducting in response to publisher requests for additional reporting capabilities. We hope these additional channels will help you better track and improve your AdSense performance.
To create new channels, just sign in to your account and visit the Channels page under your ‘AdSense Setup’ tab.