The distance between FRA and LCA is 1631 miles, before the latest M&M changes, one did acquire more status & award miles
However the costs of miles in C is a little bit cheaper than in Y (about $0.025 per mile).
One might be able to get a row to yourself in C, which gives the oportunity to sleep a little bit (which is quite nice, bc the flight is over night). In C you are asked when you wish to have dinner(after take-off or before landing), while in Y the service starts right after take-off. Y is usually quite full and the chances of having the seat next to you free (as a SEN) is quite small. As a C pax, you will be bused to passport control before Y, which makes sure that you sweep through the control (but mostly it does not matter, bc EU members get processed very quickly and the luaggage comes about 20 min after arrival on the belt).
But that is the main and, honestly, the only difference between C and Y (seats are the same, no IFE, etc)