Tagging is preference. ECBC requires chins that are shown to be tagged, though some of their field days don't require it. Some breeders have hundreds of chins in breeding, so only tag those going to the ECBC shows.
Personally, I tag every chin I show, ECBC or MCBA. Some of the chins I show end up in breeding, so they have their tags. But I do not ask ranchers that I buy a chin from to tag them for me, nor do I tag ones not from my own herd that I put in breeding.