Maybe you have noticed that I often list unsalted butter in ingredients. Mon petit ami has pointed out that you can better manage the saltiness of a dish without the extra amount added to beurre. Also, the salt manufacturers use is of a poor quality, and usually iodized, which gives it a metallic flavor. And the purpose of salting butter is to extend its shelf life; it’s for preservation. With the unsalted version, you will know whether it’s fresh (a simple sniff test will tell you right away).