My wife bought only unsalted butter at the store. I used it on my "sprouted grain" (no salt) toast one morning & it was like eating greasy ceiling tiles.
So, I grabbed the salt mill that has the Italian Artisan herbed salt in it & added a pinch across the top of the toast.
I think this is my new breakfast treat.
I use both salted and unsalted. If I am using butter as an ingredient in a recipe I will opt for unsalted as I like to control my salt levels in the dish with salt. If I am using it as a spread on toast or Bread or on a baked potato I prefer salted butter. Yes, I do keep both kinds in my fridge.