Styrene will burn smoothly, with copious amounts of sooty smoke, and it will melt easily... Resin will burn with the same smoke, but will won't melt, and it WILL sputter, and bubble and generally behave badly...
Also, it can't be stretched like styrene sprue, it just breaks... Plus, if you sand it, then sand the styrene, the difference is rather striking in the sanding dust.. There's a LOT of it with resin, far more for the same amount of sanding with styrene..
Resin dust is inert; plastic dust is inert, saw dust is inert. None is more or less toxic than the others. You're more likely to have problem with regular old house dust than any of these. When you get tested for allergies, theu don't test for resin or plastic. These are all, however, iritants, i.e., they'll cause you to cough or sneeze if you ingest them.
Ditto... Irritant, yes, toxic, no...
Resin is only toxic while it's a liquid, both as an inhalation and ingestion-hazard (the catalyst especially) and a splash hazard... It can cause chemical burns to exposed skin as well.. Don't spill it on your skin, and don't pour it in your eyes or drink it, m'kay?
Now, were you to be sanding resin parts on say, an industrial scale, eight hours a day, 40 hours a week, then air-quality standards set by OSHA have to be met and the proper safety equipment furnished and worn..
For most modeler's purposes, we don't get exposed to nearly enough of the stuff to make a difference, even over the course of a lifetime of modeling, unless you've already got some pretty bad respiratory issues t begin with..
Don't sweat it, unless it makes you feel better, psychologically, about it...