Sketches are really to provide a design. They aren't necessarily "tools" that can be used in your graphic program, like templates are. You can buy magazines (i.e., Becky Higgin's Sketches volumes) that consist of nothing but sketches, and you can also find sketches in the regular issues of Creating Keepsakes magazine and CK online (as well as on our challenge board, of course). These are for paper OR digital scrappers, because they provide "ideas." Yes, if you have a sketch online you can kind of manipulate it like nighty does, but really - sketches were around long before digi-scrapping became popular.
Hope that helps!