It seems that this post can be helpful - http://blogs.technet.com/b/seanearp/archive/2009/03/04/sharepoint-profile-cleanup.aspx. although it's about SP 2007.

Here's the citation: update to the paragraph above… commenter Chris reminded me that I was not quite right about the My Site deletion. While the e-mail itself is not related to the “Site Use confirmation and deletion” feature, sites are not actually deleted unless that feature is turned on. The e-mail to the manager is telling a fib. If the “Site Use confirmation and deletion” feature is enabled, the site is deleted due to the fact that the user never confirms the e-mail checking to see if they are still using the site; not due to the My Site Cleanup Job itself. I also came across another great resource on My Sites and disabled/deleted users from Phil Wicklund that is well worth reading: http://philwicklund.com/whitepapers/Documents/My%20Site%20Concerning%20Scenarios%20Study%20and%20Strategy.pdf)

It seems that this post can be helpful - blog link although it's about SP 2007.

Here's the citation:

Update to the paragraph above… commenter Chris reminded me that I was not quite right about the My Site deletion. While the e-mail itself is not related to the “Site Use confirmation and deletion” feature, sites are not actually deleted unless that feature is turned on. The e-mail to the manager is telling a fib. If the “Site Use confirmation and deletion” feature is enabled, the site is deleted due to the fact that the user never confirms the e-mail checking to see if they are still using the site; not due to the My Site Cleanup Job itself. I also came across another great resource on My Sites and disabled/deleted users from Phil Wicklund that is well worth reading: link