Usually it is when there are only going to be a small number of users who will ever use the application. When I say small number, I mean about 100 or fewer users. Another time to use two-tier architecture is when other applications will not need to access the functionality provided by the two-tier application. Take for instance an application that performs some function that is only needed in this one instance—you probably will not need to worry about incorporating this functionality into other applications. Because the functionality does not need to be reused, there is no point in creating a reusable component.