We tag bulls with yellow or orange and heifers get green for my son's and white if they are from my cows. Since having the joint issues, they will just get a number if they aren't tagged until we get them in at about 6-10 weeks, then I will match the calf to the cow then when it comes time to wean, the ones we keep as replacements will get a number correlated to the dam. We start with the year and go up...17-1 and up. We have 2 friends that buy feeders and they take the tags out and replace with their own set of numbers so we get back all sorts of tags. I wash them and reuse. One year I had a ton of blue tags so all bulls/steers got blue. We work the calves at about 6-10 weeks, blackleg, and usually put all calves of the same sex at a pasture so that when it comes time to gather up and sell, we have all one sex to go. Sometimes when we want a certain cow to go with a certain bull then we have mixed sexes of calves at the same pasture. But agree with all the others.... tags are important for any kind of record keeping. All the farmers in the area know that our adult cows have green or white tags, in at least one ear even if sometimes they still have the tag of another color if they were bought. Had a guy call the other day and said he had 6 cows and a calf in his catch pen, didn't think they were ours since they had red tags but wanted me to go by and make sure since they couldn't find anyone else.....they weren't ours, but..... just having the tags gave us a way to say definitely yes or definitely no....
I keep the records and it makes it easier to just look up when they have a tag, and YES some of ours have names too....