Because it is the most correct (and GAAP compliant), the unearned income method is best used when there's outside reporting or a large number of deposits/retainers involved. It's also useful when the deposit will be used over multiple accounting periods, since it doesn't require a journal entry. With snow removal, there's usually snow removed in December and then in the following year, in January. So, in this scenario, the unearned deposit method works well.