It's better if you want to optimize your ad placement. Use one custom channel per ad block. Otherwise you can simply create one url channel per site/blog and you'll have stats for each domains. That's enough for me now.
It is always better to use channels for your adsense ads. So you can simply find which ad block earned how much with the CPC and CTR.
Using custom channels also gives you the option to allow advertisers to target your channels, which in theory should result in higher eCPM/ePC ..
I agree with Tearabite. Targetable channels always yield to higher "placement ad" ratio with higher eCPM. You can analysis the result in Adsense's advance report feature.
I use channels to get more information about my ads income. Which ads click people mostly. You will find quick which ads are worth to remove and try new place to put in.
when i used channel my income are no so good when i'm not using channel...its been several days now and i'm still wondering...
Use of channels make it easier to understand which ads, which types of ads or which sites makes income. So we can optimize our sites accordingly.
i use channels for tracking purposes..when i started i didnt use them and had hard time figuring out my clicks
I use channels and it seems almost random which channel gets what, how much and when. I was blissfully ignorant when it was one big mush, now I'm informed and confused.
I could not live without channels. URL Channels are especially needed, and how can you possibly analyze anything without using channels for your ad placements.