I changed my ro membrane a couple of months ago and for a while got 0.00 out of it, this amazed me and I cant understand it. But if it had stayed this way I would have had no need for di.
As regards your question, some peeps on here say they use water as high as 10-11 ppm and get good results on glass, if this be the case and you're happy at this ppm then you won't need to polish the water down to 0.00.
Personally I only use water that is 0.00-0.01
Steve a