Playable Pitch is a feature which allows you to retune any actively-playing Samples in realtime. This is intended to allow you to write melodies and chord progressions with Samples.
For example, if you have a chord progression that goes C - F - G - C, and you have a Sample which is in C Major, you can use Playable Pitch to retune that sample to F and G by playing those notes between G-1 and G1 on your keyboard.
While playing a Sample, press any key in the Playable Pitch section of the keyboard and the audio will instantly pitch up or down based on the difference in semitones from your session key.
Note: The keyboard range of Playable Pitch will move depending on the Key selected in your session. As seen on the bottom right hand of the above screenshot, we're in G Major, meaning Playable Pitch spans G-1 to G1.