TUNABLE_INT vs TUNABLE_INT_FETCH

Hi,
I am a bit unclear on what are the pros and cons of using
TUNABLE_INT vs TUNABLE_INT_FETCH within a device driver.

As a matter of fact, as i read the definitions in sys/kernel.h
I almost wonder whether we need the TUNABLE_INT form at all.

can anyone help clarify the differences ?

thanks
luigi