For home users like you and I, none.
The main use seems to be as the default method for pooling many drives into a single large filesystem, for simplicity, so that one doesn't have to bother balancing storage use among individual drives.

But unRAID and mhddfs also solve that problem, without the same risk of losing (or having to restore) everything that comes with RAID5.

Here, I swore off RAID years ago, when large hard drives were still just a few hundred GB in size. With them now in the 2-3TB range per drive, there's just no frickin way I'd want to put up with a RAID trying to manage those sizes. Too slow to build, too slow and risky to resync, low tolerance of failure, and a real risk of losing everything. And very few people I know actually back up their RAID array.. not even Julf (who knows better!).

So instead of adding drives to the RAID for redundancy, further complicating things, I use a pair of mhddfs arrays. One is live, the other is a complete duplicate (aka. "backup"), that gets resynced periodically.

And anything I deem "critical" has several additional backups.
That's my system, and it works for me. It won't work for you, because MS-Windows doesn't have "mhddfs".

Cheers