There was a post on here a long time ago - maybe from Alex - indicating where the 'cutoff' point is between using a DI or an RO. It was to complicated for me to understand at the time and, as I use an RO because our water is a TDS of about 250, I didn't bother to try to work it out.
It might be a good thing if the Newbies might try and find it so they know what to expect.
For example, resin will last much longer with an input TDS of 20 than it would with an input TDS of say 60.
Spruce