Acetone smoothing works great...but....only for ABS. Won't touch PLA. The only things that can smooth PLA that way are pretty nasty to work with and I generally wouldn't recommend messing with them.
Since I'm usually interested in highly precise parts smoothing doesn't generally interest me since you do get some deformation and shifting of dimensions when you smooth. But sometimes it does make sense.
Like a few years ago when I made my MIDI sequencer and wanted the buttons to look nicer:
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They were functional...but just didn't look great.
So I printed them in ABS and broke out my smoothing setup. Just a plain metal paint can from the hardware store, a couple of paper towels and some magnets. Line the can with paper towels, add a little bit of acetone (just a few tbsp is enough, just have to soak the towels) then put it on my heated print bed for about 10 minutes:
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Result - nice smooth buttons!
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I'm still not 100% happy with it though. The buttons aren't super consistent and just don't look great overall as a result. But...it works and it's nicer than the rough non-smoothed buttons.