Kombu dashi is used in all over Japan, but particularly favored in the Western region. There are several different kombu on the market. Depending on the kind and origin of the kombu, the appropriate amount to use to get dashi broth from it is different.
The kombu I used here is Hidaka kombu, which is used for getting dashi, as well as stewing itself to eat. If you are using Rausu kombu or Makombu, use much smaller amount, as they brew stronger dashi.
Kombu dashi is used for hot pot, noodle soup, oden, among other dishes. It is not for miso soup, but used often for clear soup (osuimono). As the aroma and flavor of the dashi extracted from kombu is delicate, it’s better not to overwhelm it by using strong flavoring or ingredients, such as miso.
If you use dashi effectively, you can reduce the amount of sodium without compromising the flavor of food. Japanese food prepared with strong dashi contains a lot of glutamic acid, which is the source of umami flavor in kombu. Umami flavor is so satisfying, that it can compensate the lack of saltiness in food.
Used kombu after dashi is extracted can be eaten. I often chop the used kombu to thin strips, and mix them with a drop of ponzu and chopped scallions.