Whether or not I do it depends on each situation. Sometimes additional information is useful or even required to answer why the thread was closed or a vendor/provider is banned.
Other times it is just the need to express a view or opinion.
The fact is in some threads that are closed and no staff comments are added we get complaints and when we do add comments we get complaints.
In effect it takes a very short time to become insensitive to the whining, bitching, and moaning that seems to come with every staff action, especially when disciplining users. A very recent thread referencing me is a perfect example, but if no one does anything wrong how do they get warned, infracted, or banned.