Reverb?
Smooths everything out and blurs your errors. Once you get good you do not need it - just like vibrato.
I use reverb while recording multitrack, mix it, then listen to it with and without reverb. Then I decide.
Lately I leave it off unless it is a mood thing. It makes your playing crisper and you can hear detail and nuance which is the theremin's REAL asset - reverb conceals that asset.
If you play fast, staccato or pizzicato reverb hides it and kills your efforts.
Keep in mind that YOU ARE THE ASSET. You really want to hide yourself?
Sometimes. Especially now.
Rupert