RDBMS Version: 11.2.0.4
Platform : Oracle Linux 6.5
Question1.
What exactly does SHRINK SPACE COMPACT do ? When I googled , I came across the following diagram from http://fatdba.com/tag/architecture/
What do the blue lines and blue dotted lines in the diagram represent ?

Question2.
If I run just ALTER TABLE EMP SHRINK SPACE ; command (without running SHRINK SPACE COMPACT) , it will still do what SHRINK SPACE COMPACT was supposed to do. Right ? Then , what is the advantage in running SHRINK SPACE COMPACT ?