it is a special kind of rear differential that does the following: when one of your rear tires has more traction than the other, power will not be transferred to only one wheel, but the diff will lock and allow both wheels the same amount of power. in short, it keeps you on the road better in slippery conditions... and you do better burn outs
There have been many posts on this option in this and the solsticeforum.com sister site.
The main minus is the tendency of having both drive wheels break loose at the same time when under power (especially on ice/snow/rain) on a curve. Without this option, you would first only spin one (i.e. inside) wheel giving you a better indication of being near the edge of traction. When both go (spin) at once, you can quickly find yourself pointing the opposite direction and/or spinning around, etc.
For this car, if you are anything of an agressive driver, I would get it. If you are only going to cruise around, you probably wouldn't miss it, and it could keep you out of big trouble on a curve if the conditions are 'wrong'.
It does help in getting unstuck in snow/ice/mud, but this reason shouldn't be a factor in the sol/sky.
It's a LIMITED Slip differential as opposed to an OPEN diff.
When you drop the clutch and burn off some rubber it will leave 2 stripes instead of 1. Torque-sensing aka torque-biased means it senses which wheel has the most grip and sends more power that way.
The limited part means you must have at least "some" traction for it to work properly as opposed to a locking diff which doesn't need any but that is a story for a truck (or an old muscle-car...).