But if I do, will I be able to see how much each URL with Adsense earns?

Yep. Plus you'll be able to see how much you earn from your Google traffic vs your Bing traffic vs your Facebook traffic vs your direct traffic, and a bunch of other stuff.

I also use it to see what mobile devices aren't earning, so I can test to see if there's some issue in how the sites display on that device.

There's usually about a one day lag for the AdSense data to show up in Analytics so don't think you've done something wrong if it doesn't appear at first.

What's great about the per-page Adsense reporting is the things that you can pick out by looking at the long-term stats. For just one example, I used to worry about irrelevant ads showing up on pages that Google's robots were obviously miscategorizing, but using the Analytics Adsense stats I found out that many of the pages that tend to get highly irrelevant ads actually have well-above-average CPMs. Things like this are very good to know, and you can't get these stats through Adsense itself (at least for a site like mine, which has thousands of pages with the same Adsense code).

Thanks everyone! I'm looking forward to the new info.