'Nuff said.
Okay, okay. Yes, there are situations where using a smith machine would be a smart idea such as some rehabilitation applications involving partial ranges of motion, trying to overload specific ranges of motion, etc.

Only if you reach the boundary will the boundary recede before you. And if you don't, if you confine your efforts, the boundary will shrink to accommodate itself to your efforts. And you can only expand your capacities by working to the very limit.
- Hugh Nibley


"The more time and effort that people put into anything - no matter how useless, dysfunctional, or downright stupid it may be - the harder it is for them to walk away... We all justify the time, effort, suffering, and years and years that we devote to something by telling ourselves and others that there must be something worthwhile and important about it or we never would have sunk so much of our lives into it."
- Robert Sutton, PhD (The No Asshole Rule)