RO/DI water vs just RO, Is deionized water helpful or harmful in hydro?

I see a lot of talk about reverse osmosis being used in hydroponics but not deionizing just wondering if there's a reason for this. I have an ro/di filter and I keep my water ppm at 0tds . Reverse osmosis will get you about 90-96% of your water contaminants out ro/di will get 100%. But the dionizing resin is some nasty stuff. It also lowers the ph of the water a little which is helpful to me.
I use my ro/di water for other things as well, and I can bypass the di stage if need be. Any thoughts would be appreciated.