R/O less D/I anyone?

[Saltysteve]

Just wondering, I went and bought my tank an R/O unit, I mean my family
The sales rep I was talking with was very helpful. He did not want me to spend money where I didn't need to. A bit of confusion centered around the D/I filter. I have to ask, those of you that have your own units, are running both R/O and D/I or are most of you running just R/O ?

What exactly is the benefit associated wth D/I?
Thanks