It all depends on the palate and how much you actually cook at home. For someone who rarely cooks at home, a jar of sauce is easier. For someone who likes to cook and always eats at home (and the same cuisine), then it's more economical and fun to make from scratch.

I prefer a lot of variety and try to split groceries with several friends when I can. That way, the ingredients are always fresh and there is little wastage and of course there isn't that much of a storage problem as there would be if I collected everything.

As for teriyaki sauce, if you have soy, brown sugar and mirin, why add an extra bottle to the fridge?