Uses include: your signature, letterhead, commonly used phrases, … Snippets also work as file / folder templates. Create "empty" documents by dragging a file snippet to the Finder. Create folder hierarchies by dragging a folder snippet to the Finder.
Snippets stick to the edges of your screen. Create a snippet by dragging text, images, … to the left or right edges of you main screen. Use a snippet by dragging it to its target destination.