Say you are writing SQL in an SQL Commander and need to look at details about a table to get the SQL right, for instance the size of a VARCHAR column.
Instead of flipping back and forth between a table's Object View tab and the SQL Commander tab, you can place them side-by-side.
Just open both tabs and then drag and drop one of them next to the other, or above or below the other. You may even drag a tab outside the main window and it will be displayed in its own window.
You can read more about this and other ways to rearrange tabs in the users guide.