Some people with large monitors and large resolutions may prefer the larger GUI; whereas people with less desktop real estate may prefer the smaller GUI.
Both GUI's show the same statistics, and you can switch between them at any time using the View menu.
The Docked GUI
The docked UI contains the same features as the small UI with some major benefits.
Poker Roommate will only appear when a new hand has been dealt to you.
Once you win, fold, or switch to another application, Poker Roommate will sink away staying invisible until a new hand has been dealt.
If you close your poker table, Poker Roommate will go into a hibernation mode.
In hibernation mode it will use almost no resources until it has detected you have begun playing poker again.
You can dock the UI anywhere on the screen, the animation to the right shows one possibility.
The Large GUI
The large UI contains all of the features in Poker Roommate.