I spent a frustrating afternoon a few weeks ago trying to understand the differences between short-haul Y,B,H and K or L maybe. Printed out the fare rules and laid them across several desks!

For Y it was clear enough. But for B & H I just could not determine a reason to pay the significant extra for these options (I am under the impression these are the so-called semi-flex?).

What pre-planned reasons do FTers use the semi-flex for?

I know I'm likely missing something, but willing to learn