From FRA I often have no other choice than buying a full-fare ticket. One of my regular trips is FRA-AMS-FRA in one day or with one overnight during the week. LH does not offer anything but full-fare or high booking-class tix for this type of routing. And often the difference between Y and C is only about €60, so the choice is obvious.
Over a saturday night I can probably get it for under €200....