The same reasons apply to just about any standalone digital recording solution, such as the BR-8, vs computer recording. Here's some of the major differences.
Computer recording gives you easier expansion/upgradability, usually easier editing, it can be easier to master tracks and burn CDs, and there are lots of options for backing up, effects plugins, etc. It can also be cheaper if you already own a good computer, but depends on what you buy. It is harder to transport if you record at several different places. It might be more difficult to use a PC or Mac for recording if you don't know much about how they operate and how to maintain it. Even a properly maintained PC will crash now and then and really mess things up. Just know this is going to eventually happen, make good backups, and try not to throw it out the window when it happens at the most inopportune time.
Recording with a separate unit mainly gives you portability, and tends to be more stable in terms of crashing (most of the time.) It's more of a self contained solution where you can get several features in a single box, but you are also stuck with that unit's features and limitations. It's a device that is setup only for a few related purposes, and the good ones do those things very well. That's all they can do however, where a computer can be used for lots of things. Can be hard and/or expensive to upgrade, if not downright impossible.
I have used a computer for recording, and
a VS880. I prefer the computer by far for editing and burning CDs. I prefer the 880 when I have to go to a different location to record something on short notice. There's several threads that cover this topic, so you will probably find much more info by doing a search. If you aren't going to different locations to record on a regular basis, and don't mind some growing pains while you research the many options and build your computer into a solid recording unit, then the PC is a great solution.