What does it mean?
Sample rate determines the Nyquist limit and the duration of a buffer of N samples. Raising it does not automatically improve every effect's character and can increase CPU load.
Example128 samples at 48 kHz last about 2.667 ms.
How the meaning changes between controls
Audio interface
The device or engine stream rate, which affects buffer duration and compatibility.
Bitcrusher
The effect's held-sample rate; this does not change the interface sample rate.