The advantage is that you can change the device without having to change all your scripts and config files and everything else that refers to it.
For example, say you have a user home directory mounted at [tt]/export/home[/tt]. Say it's on a 2 Gig drive. When you start to run out of space, you just back up the files on it, unmount it, mount your new 1 Terabyte array at [tt]/export/home[/tt], then restore the files. Now everyone has 1 TB to play with and there are no scripts to change or config files to mess with.
The mount points are a logical reference to a physical device. This makes it easy to change the physical devices when you need to.
Plus, I don't think you CAN save something to [tt]/dev/dsk/c0t0d0s0[/tt]! On my systems, these are just links to block special devices in [tt]/devices[/tt]. They aren't directories. You can't save anything there.
Hope this helps.