Sitecore Access Viewer
Some CMS systems have an extremely granular view of content. Sitecore provides a number of controls to manage and understand security permissions. The Access Viewer is used to select a role or account (not shown) and determine what permissions they have to items. This interface is separate from that which allows the ability to set permissions.
The main reason there are two interfaces, is that many things in Sitecore can be in a number of ways; through defaults (known as “Standard Values”) on Content Item types, inherited from parents, or set manually. Given there are many ways to set permissions, having a view that rolls up all of these different levels is nessesary.