>Why do recipes call for unsalted butter, then tell you to add 1/2 tsp
>of salt?
Why not just use an appropriate amount of salted butter with
>the unsalted?

Why would you use both unsalted butter instead than combining two kinds
of butter?
That would be an added expense.
Whenever I use butter in bakery and confectionery cookery I never
bother to use salted butter , rather I add salt in the recipe instead.

>Ideas?
Generally salted butter melts faster than unsalted as salt has some
sort of melting point depression effect.
So unsalted butter is more pliable than salted butter and that what
makes it suitable for laminated pastries and in many baking
applications.
If you cream salted butter with sugar it tends to soften faster than
unsalted butter. so the resulting cream will have less incorporated air
bubbles than if the unsalted butter is used and there is a difference
in the resulting cream specific gravity which can influence the cake
quality .