Sketches and templates can be a very helpful tool to have in your scrapbooking toolbox. I use them when I put together a kit or piece a page together that someone else created. In my day to day scrapbooking though, I just don't seem to use them very much. I think I just spontaneously create my pages by looking at my photos, papers, and embellishments I am going to use.
But....I have discovered that using a sketch or template is really a great way to go when I have to create an album in very little time. When time is critical, then I design a layout and use it on every page to make it speed along. I may vary the colors or patterns, use some different embellishments, but if I keep the layout the same, I have discovered that this is a huge timesaver. It also pulls the entire album together into one cohesive design.