I've seen most in-home kegerators have the CO2 tank and regulator inside the fridge. But I remember from my bar-working days that the CO2 tank was outside the fridge. Does this really make a difference? If I had a setup that required the CO2 tank outside the fridge, how much am I losing?
No, it makes no difference - the CO2 is already liquid, and the difference between fridge and room temperature doesn't make any significant difference.
When the CO2 comes out of the tank and converts to gas, it becomes much colder - again, significantly more colder than the difference between fridge and room temp. So again, no real difference.
Where is does make a difference to some people is aesthetics - a CO2 tank in the kegerator looks cleaner from the outside.