If you ever have "power slid" your Z (either on wet road or just hammering your tires on a dry one) you will notice you have a very hard time predicting when your back end is going to "break loose", and when it does, it does so almost violently. My previous car was a 94 Miata, and I loved drifting and sliding it around in wet conditions. The Z was no fun at all. The Miata (unbeknownst to me, had a good LSD)
Enter the Quaife LSD.
Now my "drifts" are both predictable ,(not dependent on hugely variable power transfer from different temperatures of diff oil) AND more importantly CONTROLLABLE. I drift a bit in the snow and rain, but more importantly it happens if I get throttle happy at the track. The Quaife has saved me from any number of trips into the dirt.
Now when I begin to power slide, the back end goes out smoothly and controllably and comes back (with a slight throttle lift) the same way.
Its just plain fun.
I chose Quaife (helical gear style) over other LSDs due to low maintenance requirements (none really) and handling characteristics under normal use (I mostly DD my Z)
LSD is recommended (by me lol) if:
1. You plan to track. (I'd say almost mandatory)
2. you run in the wet and don't like spinning out when you push her a bit hard into a turn.
3. you don't like the feeling of the traction control/VDC (nanny) pulling power every time you aggressively turn and simultaneously accelerate. LSD vectors power to your better gripping rear wheel to avoid the spins which activate the "nanny"
4. You occasionally like to push into a drift for fun (note: for best results remember to turn off the VDC. Okay mods I'll say it... ONLY AT THE TRACK
)