I’ve found numerous versions of powershell scripts to get the last modified date of a site collection to determine if a site is being used or not. However, I cannot find any info that says what form of change needs to be made to a site collection in order to update the site collection’s “last modified” date and bring it up to the current date. Will a permission change to a site update this “Last Modified” date? Changing the site settings set this date current? Your expertise would be greatly appreciated!!
Enable auditing can be a good approach to deal in such situation.Yes, if you change the permission on site collection, it will let you show as “Last Modified date”.
To enable auditing, you may walk through this informative resource and follow the steps mentioned into this : https://support.office.com/en-za/article/Configure-audit-settings-for-a-site-collection-f5a346d0-ee0f-4412-a5e6-d9b5abaa1012
If you wish to track such changes automatically, you may also consider on Lepide sharePoint auditing tool that helps to track every changes at granular level and provides the data into real time.
