the-erc's got it, yep. By having a quantizer at the ready, there's a lot of interesting things you can do, such as scale constraint, deriving arpeggi from LFO curves, making more use of the Stages as a sequencer, and the like. It also functions as a useful on-the-fly transposition tool via its BIAS control. And, with a quantizer on hand, there's some glitchy things that becomes doable, sort of along the lines of using the MS-20's input section. By using the quantizer to "mistrack" incoming audio, and then also employing the Plankton ENVF to mess with the VCF in conjunction with that, this has loads of potential for Aphex-ish percussive glitching. Most people tend to associate quantizing with sequencers, but the fact is that they've got tons of abuse potential beyond that.
There's another twisted thing about those two modules: you can send the envelope gen's outputted CVs to the quantizer AND somewhere else...but one of those ENVF outputs is inverted, so this opens up another stage of glitching that the MS-20 cannot do. For example, you can have the quantizer deriving CVs from the inverted envelope, but FM the complex VCO via its modulation oscillator in the OPPOSITE direction. Pitch goes down as chaotic racket increases, and so on. And of course, if there's a sequencer in a future upgrade, the OP's set already.