Makes no functional difference, but an outside tank is easier to work with and reduces crowding inside. My first keggerator had the tank inside, then I moved it out and added two more taps. Both of my current systems have the tank and primary regulator outside and the secondary regulator inside.
I've got a T in the line outside, so I can force carbonate.
Remember one unassailable statistic, as explained by the late, great George Carlin: "Just think of how stupid the average person is, and then realize half of them are even stupider!"
"I would like to die on Mars, just not on impact." Elon Musk