Sometimes when you fetch an entity you're only interested in retrieving certain fields (to improve performance of the operation, i.e. list view) and other times you need a more detailed view of the data. While using separate layouts to maintain this distinction is possible, it feels clumsy and is more difficult to maintain. Ideally it would be nice if queries could be bound directly to tables, or table instances, rather than layouts. But even they were bound to layouts it would be nice if we could specify the fields to be returned in the result.