Maths is useful enough that there's not really a "not ready for" point to it. You'll get results from square 1, to be sure...and then, you can grow with it and sort out some of the other ridiculous amount of things it can do. Joe came up with a solid winner with that thing.
As for negative and positive voltage values...keep in mind that those terms can be a little deceptive, because you can shift a "negative" into positive voltages by adding a DC offset. The real importance here is that you can INVERT positive-going signals into negative-going ones. And those inverted signals have some amazing uses...
My JP-6 has inverted envelope settings. And those are, quite often, key to getting that Jupiter-6 sound. By modulating the VCF with a negative envelope instead of a positive one, this inverts the cutoff behavior...allowing attacks to LOWER the cutoff instead of raising it. And if you want a wild, sweepy thing to happen when you RELEASE the keys, that's how you do it. In modular, this just ups the abuse potential. For example, let's say you want to pan something...but you haven't got a panner in the rig. The proper fix would be to use two VCAs, an LFO, and an inverter so you can get a 180-degree negative of the LFO's output. You'd split the LFO's output, with one going straight to one VCA's CV, but the other wouldn't get a straight CV, but one routed through the inverter. The result is that as one VCA is opening up, the other is closing in perfect sync, and if you hardpan those VCA outputs to the left and right...well, there you go!
Whenever you run across something that's very much on the "basics" level such as that, you can bet even money that that's a functionality that MUST be in a rig...no matter what it's intended for!