Originally Posted by
ekozie
As a flyer, there is no functional difference in I and C classes. On the flipside, from the airline/industry/GDS perspective, each fare bucket for each flight and each route contains a multitude of published fares, which have different rules, prices, surcharges, validities, etc. Having the many, many fares that are published for each possible flight/route stratified into buckets (i.e., classes) makes identifying fares according to the hierarchies of price and restrictions slightly easier. Classes are also relevant to flyers in certain circumstances, such as SDC on a domestic coach ticket.
I would disagree with this example. While C isn't unrestricted last seat availability, it's generally in most markets a fully flexible and fully refundable without penalty business class fare, unlike the D I Z fares that generally have change fees (typically ranging up to about $500 for TATL/TPAC RTs exUSA, but this depends on the market) and generally aren't refundable (as a credit to the original means of payment).
Moreover, some I fares have advanced purchase and minimum stay requirements while C fares generally do not.