the smith machine is just another tool in the gym. It can be used both effectively and ineffectively. I wouldn’t want it to be my only option for squats, but if that’s all I had, it’s a hell of a lot better than nothing.
Outside of leg work, I’ve found 2 reasonably good uses for the smith machine. I’ve used it for some overhead press work. Meadows is a fan of it. I haven’t done this in awhile because I do so much overhead pressing with odd objects for strongman, but it would work. I still use it from time to time for bent over barbell rows. I do enough other stability work that when I do barbell rows, I usually just want to work the back, and the smith machine is good for that. The guided bar path is fine for that lift.