Thank you.
The most common use is to control electronic instruments. You can play instruments and control effects (similar to MIDI).
If you are a programming or electronics enthusiast, the uses are limited only by your imagination. You could turn a crank to adjust the lighting in a room, open a garage door, or rotate a tank turret.
In short, the Playdate becomes a versatile remote controller. OSC is widely used in such fields, and it can be implemented at low cost using existing libraries.
There are many OSC clients available, but one with a physical crank is likely unique.
(This is not my first language, so please excuse my poor English.)