Use the Compare wizard to:
Examine the permission settings in relation to another SharePoint object.
Find out which permissions should be given/taken to the preferred SharePoint object users in compare to another similar SharePoint object.
Compare SharePoint object permissions for the entire history by selecting the same SharePoint object for a different time period.
Click the Compare option. The following Compare options are available:
Compare to Parent – available for sites with broken permissions only. Choose this option to compare differences between the selected securable object and its parent.
Compare to Previous – available when there are previous permission records for the selected securable object. Explore how permissions for a selected securable object have changed over time. This is the only available option if you have selected the securable object that doesn't have broken permission inheritance.
Choose a certain permission record by the date you want to compare from the dropdown menu. Select a site collection, then drill down to the site, subsite, list and list item. Do this on both sides to compare the permissions for selected objects. You can click on Same Target as Source if you want to compare the same securable object.