But Sorters don't have to be placed on a belt. If two buildings are close enough, you can also directly connect them (depending on their type). This means you can have, for example, a Sorter which takes completed products from an Assembling Machine and places them directly in a Storage Building; or takes these same products and places them in another Assembling Machine where they're part of the recipe for an even more complex product.
Every building which can attach to a Sorter has predefined points where a Sorter can be attached to them. You'll see these points when you hover over the building with a Sorter in your hand. Your cursor will snap to the nearest one of these points automatically. Some buildings have a more limited number of Sorter snapping points, which means you'll have to think about how best to place Belts and Sorters around them.