My car never had it and it wasn't missed. I did my black interior conversion last year and all of a sudden I was wishing for A/C. I think it depends partially on your interior color for some of us.
Technically even though the AC pulley is free spinning, a longer belt does equal more drag, but it's such a small amount that you wouldn't feel it. The biggest gain is the weight you drop off the front end. It's one of those things that is a small mod but when you add it with other things it can make a difference in your time at the track if that's what you're looking for.
Hmm I guess I like it because after spending a week in SC and enjoying the car on every hot day, I would just enjoy it that much more. I remember the days driving girls to the beach in the ice cold air in the Mustang... now they don't even want to suffer on the ride down without it (I just take the Audi though).
I took the a/c off my wife's daily driven 90GT, and she/we don't miss it. In TX. It just quit working one day and I told her I would fix it, to which she replied:
"No, just take it all off, get the weight off the nose."
if you decide to keep it, try and find a friend or someone that has a liscense to buy r12 refridgerant. it will get colder than 134A, but you need a license to buy it and its expensive....