I am installing a new dishwasher with a 12-2 wire and breaker. Do I need a cut off or switch near the dishwasher? Thanks.

The main advantage of having a cutout near your dishwasher is convenience -- if

You have a problem with the dishwasher you can quickly turn off the power -- it is

Also convenient to have a cutoff, close to dishwasher when it needs repaired...

I worked in industrial maintenance where a cutoff was locked out -- while a motor

Was being replaced or work being done on the electrical wiring... SAFETY!!

Yes, a service disconnect is requiured. This can be a toggle switch above the counter, or below under the sink, or can be a cord with plug and a receptacle.