I am trying to find out all of a complex site permissions. Those varie depending of the sub-site and I want to make sure 100% are reviewed so the best way would be to have one report and to mark it as we go down. The only solution I know of involves going through the sub-sites one by one and look at the permissions - that's what I am trying to avoid.
This is a tool I developed to list all permissions with site structure for a SharePoint 2013 site. Works with SP 2010 as well. https://sppermissionanalyzer.codeplex.com
Hope this is of some help.