Individually controlling the power management behavior of your LAN adapter

A co-worker recently showed me another (yes, yet another) place in Windows 7 that I hadn't visited before:

1. Bring up Network and Sharing Center, then find your Local Area Connection


2. Click on Local Area Connection to bring up Local Area Connection Status, then click on the Properties button.


3. In the Local Area Connection Properties, click the button near the top labeled Configure...


4. You'll be taken to a new box labeled (something) Network Connection Properties.
   

   
   Bwaa-hah-hah-hah-HA! You thought you were working with your connection properties, but now you have found your connection properties!
   
   You are in a maze full of network properties, all alike...
   



5. In the Network Connection Properties dialog, you will now see a tab labeled Power Management


6. In the Power Management tab, you will find a checkbox:
   

   
   Allow the computer to turn off this device to save power
   

On my machine, at least, this box was checked by default, which surprised me. I have a desktop computer! Why does Windows think it would be convenient or useful to sometimes turn off this device? Does it use a significant amount of power to keep my LAN network adapter running? I guess so...

Anyway, the point of this post, other than possibly letting you know about Yet Another Corner Of Windows 7 That You Haven't Visited Before, is to note that, although I found this checkbox, and I unchecked the checkbox, I am still a bit puzzled: how can I tell if this has had had any effect?

That is, how can I tell when Windows 7 has turned off my network connection device to save power, and how can I tell when Windows 7 has turned my device back on?