Here is how I am using this:

1. Install the add-on.

2. Panic that it has deleted all "not open now" websites' cookies.

3. Choose the option to "Suspend Operation" via the add-on icon.

4. Repeatedly "Undelete" all cookies until it's all done.

5. Keep the add-on suspended.

6. Now, for the next few days, I will browse like normal, but will remember to "whitelist" the websites I like to stay logged-in (Hacker News, Webmail, etc.) by clicking on the add-on icon. Remember, it is still "Suspended".

7. After a few days of usage (and when I've re-visited enough number of my regular websites), I will "Resume Operation" on the add-on, where it can start destroying the rest of the cookies like anything.

I think the "Training Period" above in point 6 should have been by default. Somehow.