I can speak for the guys who are AU NATUREL..
Smell wise, if you are a clean person, there wont be any difference..
Those who still have all their skin are more sensitive in that area.. So during sex, its that much better. Proven in studies and confirmed by a friend who had it cut at around 17yrs of age.. Thanks to that greater sensitivity, the pleasure is much more and you have better controle (like driving a car with a very responsive suspension) you can better adjust to achieve your goal (My buddy regrets doing it..)!
The only real problem some fellas have, is that the opening can be of a limited size.. So when the muscle is pumped, pulling it out of the case isnt always obvious.. And can be painful.. Unless you wait for natureLUBE, after which its gets out much easier.. Or if you know you'll be doing something, you just make sure to get it out before the muscle is pumped..
I have no intention of cutting anything except my hair and nails..