I have not used it myself, but we do have it here in our office. It does do some very cool things with ducts and pipes, etc. If you are just using plain AutoCAD and drawing dumb 2d lines, then it will definately have some benefit, because of the "smartness" of it.
For example, if you draw some duct work at a certain elevation, and then you draw some more at a higher elevation overlapping the lower one, it will automatically hide the lines of the lower duct where they cross. One down side is that there is a big learning curve.
Sorry I can't elaborate much more, but I just don't know the product itself very well.