SharePoint 2010: Confirm site use and deletion. How to restore Site Collection ?

One big part of  the migration to a new version of SharePoint is a preparation phase.
This phase emphasizes cleaning or pruning the environment before moving content database (  in case of SharePoint 2013 Upgrade you don't have in-place upgrade option) to a new version.

I recommend to clean from top to bottom.
First, identify unused web applications. (SP Migration: Phase I "Cleaning". Unused web applications )
Then check unused site collections.
At this step, I recommend to make use of "Confirm site use and deletion"

Of course, you can still use this option even you are not planning the upgrade but still feel urge to get of rid of "dead" structure and content.

I found a useful article that explain in detail how this feature works - A Closer Look At “Site use confirmation and deletion”…
As this post mentioned, it's good to know that :

As of the June 2012 CU for SharePoint 2010, the Dead Site Delete timer job now calls proc_DeleteSiteAsync which is explained below - this is good news, and now means that sites deleted by site use conformation and deletion will be subject to the site Recycle Bin.

Let's explore June 2012 CU (build 14.0.6123.5002):
It has resolved issue 2598348 Description of the SharePoint Foundation 2010 hotfix package (Wss-x-none.msp): July 2, 2012

From http://support.microsoft.com/kb/2598348

If a site is deleted by a dead site delete timer job, the site is deleted permanently. Instead, the site should be sent to the Site Collection Recycle Bin.

So, based on this knowledge you can now check 'Automatically delete the site collection if use is not confirmed' with less struggles in your mind.

And btw, Where is Site Collection bin? Here is the asnwer:
SharePoint 2010: SP1 Site Collection Recycle Bin (en-US)