I put rear discs on my D44 because:
1. Drum brakes are so antiquated. They look like something that should be on a Model A.
2. Ease of maintenance. Although a well-maintained drum brake system will brake very well, it can be difficult for the average Joe to get it set up just right.
There are so many little pieces that comprise a drum brake system. I know that I have trouble being confident that I have everything installed properly. Plus, have you ever shot one of those springs across the garage? 
Changing the pads on a disc system is much easier and quicker than replacing the shoes on a drum brake system. Discs are simpler and easier to maintain. There are far fewer moving pieces involved.
Braking performance may or may not have improved. I honestly can't sure with certainty. But purely for the reason of maintenance, disc brakes win hands down.
I've twice seen the internals of a rear drum on a Dana 44 implode. Last year on the Rubicon Trail, one of my friends had a catastrophic failure. The brakes shoes and lever were bent beyond repair. He had to crimp off the brake line and continue with no rear brakes. He got replacement parts once we reached Tahoe. We still don't know the cause.
Then my buddy had a rear wheel stud back out slightly on his alloy shaft. The quarter inch that the stud was sticking out completely wiped out the entire shoe/spring assembly. Sure that one was avoidable with proper maintenance. But he didn't even know that was a possibility, so how can you take steps to prevent it?
I currently have Explorer rear disc brakes on my D44 and they work very well, even with the MJ's stock "distribution block". I have a ZJ 4-disc prop valve to install in place of the distribution block...whenever I get a chance.