Originally Posted by
MikeBOS
The other difference is that if something goes wrong and you are put on a different flight in coach, they don't owe you anything. And some agents get confused about whether it is a paid first class ticket (it is) vs. a coach ticket with a free upgrade. It matters when determining the order of upgrades on your rerouted flight.
They usually book into "I" for biz (on rare occasions "D"), or A or P on 2 class flts. Although the underlying fare is usually a Y or K basis.
For reaccommodations, I've always suspected that "I" was accommodated in premium cabins above others ticketed using upgrade instruments booked into C, A, X, or R rebooking priority. Perhaps someone with more first hand experience can confirm that.