CV is “analog” so there is much more resolution (theoretically unlimited but we all know that physics imposes certain boundaries for practical use ), both in time and freq domains compared to MIDI. However, this also means that stuff like sysex etc is usually not implemented for CV i/o based systems (although I suppose you could use CV signals for encoding digital data as well?).
Cats with a lot of experience working with modular synths can probably explain all this in more detail…