Dashi is primarily used as a flavor enhancer, infusing umami and a briny element to dishes. In Japanese cooking, it's often used in soups and stews, and dipping sauces (e.g.,tempura sauce and tsuyu). I recommend using dashi whenever you are looking to add a briny element to a dish. For example, adding a little dashi to a fish based stew or a paella would round up the flavors nicely. Or I like to add a couple of splashes when cooking vegetables to give them depth of flavor. Mixing a little dashi powder to a mayonnaise based dip or dressing also gives it a little extra oomph.