There are times when I tackle something that I haven’t looked at for a while—for instance, a mobile project, after I’ve been immersed in designing web experiences—and a stencil or template like this might be good for reminding myself of the conventions and such for that medium. These things are constantly changing too; as Apple and Google refine and tweak and reinvent their respective views on how interacting with a mobile device should look and feel, so my own thinking and approaches to solving interaction problems evolves.
So yeah, they can be useful, for inspiration, for reminders and ideas. But it’s also too easy to throw a cookie cutter solution at a design problem because it’s there. And it may not be the best solution. As long as you’re wary of that, embrace templates, by all means.