It's been said time and time again that registered horses have (albeit slightly) better chances at a life that doesn't involve a double-decker slaughter-bound trailer or a rescue. Of course, they don't ALWAYS have the glamorous life... but registration papers CAN and DO make the difference sometimes.

Also, all those super-fun shows which folks claim to love to compete in... American Ranch Horse Association (requires registration in a stock horse registry), Foundation Quarter Horse shows, any breed-level shows... all require registration.

So, I guess if you want a 4-H horse, or a horse to do open local shows, or if you just plain don't feel like registering your cutting horses or barrel horses and only show NCHA and NBHA(which sounds silly, but I suppose it could happen)... or if you're a team roper.... an unregistered gelding would be just fine.

Otherwise, registration papers are a good thing to have.
A great deal of intelligence can be invested in ignorance when the need for illusion is deep.
Saul Bellow (1915 - 2005)