Regarding Showing: It's a ruleby the American Rabbit Breeders Association that all rabbits have to have a permenant tattoo in their left ear to be shown. Imagine having 20 Black Mini Rex Bucks on the table at one time. How would anyone be sure they got back their rabbit? How would we be sure which rabbit won? And if it wasn't a permenant tattoo, what would stop someone from changing a number every time they show? How would we keep track of how many times each rabbit won (and if it's a Grand Champion)?
Regarding ownership: By tattooing my rabbits, with my initials and a number, I am sure where each rabbit is going when it leaves my barn, I will usually find out ifit gets sold again, or if it gets dumped in the local dog pound. (And I can usually get it back!) It's a great way to identify your rabbit (and prove ownership) if a rabbit is stolen or gets loose. (Instead of saying I lost my brown bunny", you can give a tattoo indentification.
Regarding pedigrees: I can be sure of the parentage of every rabbit in my barn. I can track genetic problems and tendancies, health issues, life spans, birthing records, etc. of every rabbit I have.
It takes me about 2 minutes to tattoo a bunny. 2 minutes of discomfort is worth a lifetime of security.