I never noticed that....damn and I thought I knew everything.
In most of the other area's of wordpress when they give you the option of adding a description basicly they are giving you the ability to add a title tag. Having just checked that's what happens when you add a description.
I'm rambling on...and on....and on...and not really addressing the question.
No I don't use them but I probably should and may go back and edit all my blog categories.