Alright. Where to start, lol. For one, it takes stabilizers out of the equation. Having strong muscles + weak attachments makes you an injury waiting to happen when doing any fuctional activity, whether you're a professional athlete, or helping a friend move into a new apartment or playing softball in a beer league.
The bar is in a fixed and unnatural plane of motion, so the Smith is not even a good way to 'teach form to beginners' since no free weight movement is even executed in such a manner.
Those are the reasons the Smith is bad for both bodybuilders and recreational trainees and not just bad for athletes. So, overall it is a worthless peice of crap. In almost 14 years of training, I can proudly say the only thing I have ever used the Smith for is to stretch out on the frame after my workout. It would make a good spot to dump your gym bag, but too many people use it.
In my opinion, the world truly would be a better place if Smith Machines were never invented.