For different projects usually but there is no one answer. I use one just for my Vanners. One for cross breeds (when I feel like working on them) and a different one unicorns and unicorns "fails"

But you can use them however you want. Maybe you use them for horses you bought vs. Bred or maybe for the day of the week they were born.

Basically it is up to you

To mark specific groups of horses. For instance, my donkeys and Lusitanos have their own affixes - while the main group of my horses get a general one.

Whoops I forgot you can't change an affix unless you are the breeder. So if you buy a horse with an affix it will ALWAYS have that not matter how many times it is bought and sold.

Its wholly up to personal prefereces but the most common reasons are to label different breeds of horses, different types of horses (one for unicorns, one for donkeys etc), different BMIs (for GA horses, pegasus etc), and team affixes!

Ooh I get it, thank you for answering!