The benefit is purely on your time and wallet. All a starter really does, particularly with dry yeast, is to increase your cell count. You could make an argument that it confirms yeast viability too, but I haven't heard a whole lot of reports of dry yeast packets never taking off.
Anyway, that said, you just have to evaluate whether it's worth it to you to spend a few bucks extra to pick up an extra packet of yeast when you need it (as stated above, go by mrmalty or yeastcalc, both good sources) or to invest a few more bucks up front in a stir plate and then use a buck or so worth of extract to get a starter going, and maybe 45 minutes of your time to boil, chill, and pitch it whenever you want to do a bigger brew.
For folks using liquid strains, where vials/smackpacks run $8-12 depending on your source, and a single vial/smackpack is rarely ever enough, this is kind of a no-brainer. For folks, like you, using dry strains, it's a closer call. Totally up to you.