Adding DW to VG is really nice if you like me don't like the taste of PG, or of course, if being intolerant to PG. DW thins roughly 4 times as much as PG, so adding 10% DW is roughly like a 60/40 VG/PG mix viscosity-wise.
I started with using 20% DW, as was used by others avoiding PG, like Kurt and Cyrus Vap etc. Later, I felt it was too much, or maybe it was because of equipment change, I dunno, but now I use around 8% DW.
As said by the OP, you don't dilute the flavor(common misconception), but account for the DW in the recipe, meaning e.g. 3% flavoring is 3% flavoring regardless of using DW or not. You cannot taste the DW at all. It just thins the liquid so it's not as thick and wicks better. Also it takes the edge of the VGs sweetness, just like nic does. Lastly it lowers the boiling-point so it runs hotter at the same wattage and some feel improved TH.