I've ran into a couple of examples of how buttons are used as interrupts.
Only in a most awkward and unnecessary manner. Interrupts are cause by external events, like serial data arriving, or by things that happen very frequently, and need to not be missed, like encoders rotating.
If a switch is connected, it should be polled in loop().
Analog devices do not trigger interrupts, because the time taken to read an analog sensor is so long, in terms of how many times loop() could loop, that polling is fast enough.