I suppose a lot of reverb units were just for show, yet there are some practical uses. If you were to find a recording to be a bit "dry" (recorded without reverb, or without enough in some way), you could always add it or boost it up for a more potentially lifelike sound.
I have a few different devices that do this in different ways...the oldest of which is a spring-type Pioneer "reverberation amplifier". I find its reverberation to sound a bit "shallow" and silly as compared to some other units I've tried.
Next up is an IBM Audiovation sound card using Q-Sound processing performed with an Mwave DSP. This works well, if you don't mind the fact that it consumes lots of DSP memory and therefore hampers what you can do with the card.
Finally, I have some RadioShack stuff with reverberation or "stereo enhancement" onboard. The first is an early 1980s Archer brand "video sound processor" with several functions built into one--a matrix decoder for use with early surround sound efforts, a
Dynamic Noise Reduction unit, something that creates "stereo" sound from monophonic (which seems to be broken and makes the audio go out of phase if activated), and a stereo image enhancer.
The last piece is a ten or so band Optimus equalizer with an IMX stereo expander whose level can be controlled. It really only works well on stereo tracks, but in some cases the effect is striking and really does give the music a "live" feeling. There are some songs that this works well for and others where it does not.
Out of all of these, the two RadioShack pieces seem to work the best of anything I have tried. I've heard Carver's Sonic Holography applied to a live web stream and also liked it.
One thing I learned along the way in my audio journey thus far...
never drop a mixer with a built in spring type reverb that is turned on in the chain, no matter how mad it makes you.