"Time stretching" a sample

[Railster]

Hi guys.
Yesterday I was making a beat on the sp-303 (http://www.youtube.com/watch?v=q9XGokxnnY0) and when I was editing the start/end of a loop I found out that the first knob is adjusting (force) the timing of the selected loop.
So you can halve the Bpm of it doing a kind of time-stretching, It can (maybe) helps with looping (freezing) a note for longer time.

Any experiences about this?