Sharing has always been one of the strong points about SharePoint, but even with that there were some challenges with doing it as quickly and easily as we would have liked in SharePoint 2010. Some of the things we wanted to improve up included granting access to a site. Some of the problems here are that most end users wouldn’t know what rights to grant to someone if they could, and most users can’t see what other users have access to a site or library or list anyways. There were also sometimes problems when a user that did have rights to grant access to others would not completely understand what rights were associated with different SharePoint groups and so they would grant different rights than they really intended.
