There is a big difference between a fully locked rear, such as you get by welding the spider gears or using a spool, and auto locking rearssuch as Detroit Locker, Torsen, etc., that allow a wheel to turn faster than the other when going around a turn. A fully locked rear will make the rear wheels turn at the same speed no matter what condition and force the car to go straight ahead, whereas the limited slip or auto locker type will only lock the rear wheels when going straight ahead, or when one wheel is losing traction.
Fully locked rears are only useful in drag racing, and even there you have to be careful not to brake an axle, or you wind up making some uncontrolled turns toward the side with the broken axle.