The nose knows!
Like so many other dog sports, Barn Hunt is a recreational variation of an actual practice. Anyone that lives in the country knows how important it is to keep mice and rats from taking over your barn and other buildings. A dog that can hunt rats is worth their weight in gold.
Almost all dogs are capable of doing scent work on this basic level. It's great for the dogs and it's a fun way to let them exercise their natural instincts.