Delegate permissions vs. Folder permissions

When I want to grant someone permissions to my Exchange mailbox, I found that I can either do this via the Delegates options dialog or via a right click on the folder-> Properties-> tab: Permissions.

I noticed that the people for which I set the permissions per folder do not show up in the Delegates dialog. Is that correct?

What are the differences between setting the permissions via the Delegate dialog and the Permissions tab?