Mainly because you won't have to write as much glue code.
1) Removal of the need for complex glue code (filters, callbacks, etc.). This is nice so less sophisticated users can develop dashboards.
2) Easy hosting / deployment. I don't want that in the same system (I use dash in my own apps, and it's nice I'm not tied to much of anything else)
That's me extrapolating from a little bit of poking. I could be wrong.