I find that the beep is not all that loud and the radio can cover it.
In reality, so far I have only heard one good reason to disable a seatbelt alarm. It came from someone who drives on Frozen lakes. and wants to insure a fast escape in case of an emergency.
The Simple answer was get a seatbelt extender and leave it pluged in.
That being said, Last time this topic came up,
Disable seat belt alarm on 451???? it turned so ugly the thread not only got locked, but was pulled from the site. So be carefull out their.