I only buy unsalted butter, too - at least in stick form. I also buy salted spreadable butter for toast and the like. I really don't use stick butter for much beyond baking and to drizzle over popcorn, and I always add a bit of kosher salt to the melted butter before I drizzle it over popcorn. Distributes the salty flavor better that way.
So I'm certainly not opposed to adding salt to unsalted butter when I'm using it as a condiment or sauce. I just wasn't sure if there was some unspoken rule against using salt in compound butter, or a strong reason against it, because twice now I've come across recipes or formulas that don't include salt. I don't have much experience with compound butter - I've only made it once before, with roasted garlic, for a Mother's Day dinner. I followed the recipe, not adding salt, and when I tasted it just before putting it on the table, it tasted bland and ...well...unsalted, lol.
I ended up sprinkling sea salt on top before I put it on the table, but it still tasted a little flat. Salt makes other flavors come alive, you know? I'm not looking for salty, just - what's the word I'm looking for - vivid? I think I'll try it with just a bit of salt and see what happens. Thanks again for the replies.