You can technically eat pork at 165° Fahrenheit. But this isn't doing justice to the pork shoulder/pork butt for all your hard work. At 165 degrees, you will have a chewy mess.
When you are slow cooking a pork shoulder/pork butt, the internal temperature is rising. There is a good amount of fat inside pork. This is where a lot of the flavor of a pork shoulder comes from.
If you keep the pork shoulder/pork butt on until the internal temperature is 195 - °204° Fahrenheit, this will allow the fat to melt and render into the meat and have the pork melt in your mouth.