It performs extremely well; lead glazes can be fired at lower temperatures, produce smoother and glossier finishes with fewer flaws, and prevents crystallizatio

It performs extremely well; lead glazes can be fired at lower temperatures, produce smoother and glossier finishes with fewer flaws, and prevents crystallization (that's desirable in some glazes, but you don't want it all the time). I'm probably forgetting a few other benefits. Of course, toxicity means that it pretty much isn't used any more, so alternatives have been developed. They're just harder to work with.