Script Download:ModifyUserPermissionForAllWebsUnderASiteCollection.ziphttp://gallery.technet.microsoft.com/scriptcenter/Modify-User-Permission-for-4f7b1bfc
In a real world, grant user permission is a basic task for SharePoint Administrators. And the sites in a site collection usually have unique permission, if we need to grant the user permission for each site manually, it will take a lot of time to complete and easily miss some sites, so the SharePoint Administrators are finding a way to reduce their workload.
You can find more All-In-One Script Framework script samples at http://aka.ms/onescriptingallery