How good/bad is your source water?
It can be used , but is it better to use it over tap water...it depends.
If you have clean tap water & a sanitary RO/DI with new filters I say yes but your RO/DI should be flushed, sanitized, & hoses changed (especially the waste water hose) regularly.
My BRS value plus 75gpd is 4:1 (it wastes 4 gallons to make 1 gallon)
So my waste water will contain 5 gallons worth of my tap's TDS in 4 gallons of waste water, make sense? But it has gone through the sediment & carbon block so it is de-chlorinated & tastes better.
I have a splitter & valve on a separate line before the DI stage so I can make RO drinking water.
I use the RO for most my drinking water & baby formula etc.
I use the waste water for making coffee with, watering plants, laundry, freshwater/planted tanks etc.