I initially ran a welded diff in my S13 for drifting and it does the job but it's still not as good as the proper 2-way LSD I fitted later. The LSD gave more control through transitions and made the car more predictable. It was easier on the driveshafts too!

I ran a locked diff in my 510. It's great for drag racing but that's about all. It actually drives pretty well on the street but you have to treat it with respect in the wet. I don't think I'd ever recommend it. When my SR goes in I'm fitting an LSD with it. Car's with IRS like the 510 can get away with an open diff up to reasonable power levels I find but live axle cars are just plain annoying, spinning the inside wheel out of corners. To a degree running lots of roll resistance up front with a soft rear setup helps a bit but I think for anything with a bit of go an LSD is essential.

The only car I've had with a locker is my AMC Javelin. It's really very agricultural

-Ed