A few very good reasons:

You can have each of your account names rememberd into all the wow folders.

You can set your 'box' chars in a standard different resolution to your main player window. Same goes for sounds settings.

I'll make a little 'how to and why' post later on about this cos I didn't really found info about this on the forum .... Xzin has post some really good stuff, but 1 post for us 1 PC'ing guys would be nice :wink: