Songsmith is designed to take a melody you sing (record), then figure out a chord progression around it, then give you an arrangement by using PGMusic provided styles.
It will definitely give you some weird results, since the chord progression is based on what you sing (good, bad, or indifferent).
I bought it a number of years ago (it wasn't very expensive) along with the additional PGMusic styles, but was never very satisfied with the results. I've still got it on my computer still, but never use it. I don't think its core functionality has been updated in a very long time.