In all seriousness, there can be occasions, particularly at outstations, where the tag is useful - ground crew easily identify and a) don't hassle for checking in hand luggage at gate or b) usher to the front/priority queue.

Doesn't happen often but I have seen that for others (not me) at LCY and places like HEL where they assume everyone in Y and hasn't travelled before. Even more the case for *A (those massive LH Senator red tags) since they can be even more strict on luggage allowances.

Otherwise I don't see any benefit on hand luggage . Some do, some don't, up to you. So long as don't act DYKWIA then it isn't. Check-in luggage for identification purposes perhaps is useful.