The Sloop speed slider lets you control how often Sloop tracks the mouse and switches amongst windows and applications.
If the slider is set to fast, Sloop will track the mouse frequently and there will be a small delay between the time you move the mouse over a window and switching. If the slider is set to slow, Sloop will track the mouse less frequently and there will be a longer delay.
These speeds are relative and actual times vary depending on your computer setup and which applications are currently running.
Important point about Sloop speed!
The faster the speed, the more frequently Sloop tracks the mouse. Therefore, when the speed is fast, Sloop uses more background processing time and tends to "hog the processor." So, in general, when Sloop is going faster, your Mac will run slightly slower.
If you've noticed that Sloop has slowed down the overall performance of your Mac, it may be that the speed is set too fast and Sloop is hogging the processor. You might want to try reducing Sloop's speed in this case.