+1 on not running RO/DI straight to the sump. As already mentioned, if the valve gets stuck open it's going to be bad. Also, roscoe is correct that when RO/DI sits idle, there is some TDS creep that occurs within the membrane/filters. For that reason, it is recommended to purge the water in the membrane/filters if possible (flush kit works great for this). Another reason not to run straight to the sump is your RO/DI unit will be on & off in small short burst, which I understand will degrade your filters faster than if you run it less often but producing more water during each run (for same reasons of TDS creep).
HTH,
Rob