One note here: VCAs that are able to affect CV and modulation signals should be LINEAR and also DC-COUPLED. These are sort of workhorse VCAs in a build as you can use them for basic audio amplitude control AND CV/mod control. But these need to be linear because if you change a voltage by a given amount, that amount needs to reflect the CV scalar system. Case in point: let's say you want an LFO to sweep a VCO by a 5th on one sequencing point, but by an octave on others. With that, it's just a matter of calculating the voltage change needed, then sending that from the sequencer to the VCA. Easy-peasy.
Now, what EXPONENTIAL VCAs are about is 100% about audio. Since we perceive "apparent loudness" on an exponential scale (phons), we use exponential VCAs so that an incoming CV or mod signal can affect the thruputted audio on that same scale. Also, VCAs for audio usually are AC-coupled...they cannot pass voltages down in the subsonic and/or DC range. This is useful because DC + amplifier + speaker = And this is ALSO one reason why transformer-balanced output modules are also useful, because they block the same subsonic and DC signals.