There are many reasons to fly in a class above coach:

-- You are rich and can afford it. If you've got money to burn and hate to be uncomfortable in the slightest, it might be worth it to you.

-- Your company pays for it. Some companies have the policy that if the flight is more than "X" hours, they will pay for some better class than coach. The person arrives more refreshed and able to "hit the ground running" instead of needing 8 hours of sleep. Productivity might justify the extra cost. Employees might be more willing to travel long distances and seek out new business opportunities if the trip itself isn't such a torture. If a person is going to close a million dollar deal, then the company might not care whether it spends $2,000 or $8,000 to get the person from here to there and back.

-- You can get a free or low cost upgrade. Again, this is a balance between the actual cost and the comfort level. Obviously, if the cost is zero, or even if you only have to use up some upgrade coupons that were given to you as a result of other travel, you'd want to use those upgrades before they expire.

I love Southwest and fly them often for destinations under 3 hours. But, if the opportunity comes up to fly another airline and I can fly in domestic first class, business class or international first class at little or no cost to me, then I will.

Traveling internationally, I've had the opportunity to go in business class. For something like a 14 hour trip to Australia or the far east, or even for a 6 hour trip to Europe, I'd very much like to go in business class, if I could buy a coach ticket and use miles to upgrade, or use miles to get a business class ticket with no out-of-pocket cost.

Part of it is just the experience -- like going to a fancy resturant instead of going to McDonalds. Both serve "food" but one is just a lot more fun than the other. Why eat lobster when you get the same number of calories from hamburger?

Some airlines (United, specifically) also will tag your checked bags with a "Priority" sticker and they are supposed to come up first at the baggage claim area. That by itself wouldn't be a reason to fly in first class, but its an added benefit (when it works).

Airlines that fly international have lounges that are a nice place to be between flights, and you get free access to those lounges if you are flying in international business or first class.

In short, if you can fly in greater comfort (and yes, it is a lot more comfortable!) at little or no cost to you, or if you've just got money to burn, the upgraded classes make sense.

(this post moved to TravelBuzz from Southwest Rapid Rewards)