OK... An old fashioned mechanical timer is nice because it's easy to set and easy to re-adjust... In the kitchen I prefer it to pushing buttons.
The problem with a pot is, it doesn't move automatically as the time counts down. So for example, if you've got the pot set to the maximum, or nearly the maximum, you can't add time.
A rotary encoder doesn't move automatically either but it rotates more than 360-degrees so you can always increase or decrease the time while it's running. (My friend had an oven with a small rotary encoder to set the temperature and it was super handy.) With a rotary encoder you can also add some intelligence or "acceleration" so that fast-rotation makes big changes and slow-rotation makes small changes.