There are two persons in conversation; therefore, four possible possibilities.

The Dominant may want to be addressed as "Sir" or "Ma'am" because of their general status or NOT be addressed as such because they do NOT have a relationship with that sub/slave.

The sub/slave may want to use "Sir" or "Ma'am" because of their general status (and training) or NOT use it because they have no relationship with the Dom/Master being communicated with.

So, the Dom has preference and so does the sub/slave.

I tell sub/slaves with whom I do not have relationships that they do NOT have to address me as Sir since we do not have that type of relationship but that if they choose to do it for their own reasons, it is OK with me.

We are all happy. So, Sir and Ma'am is NOT overused in my judgment.