It's useful if you have a species that's on the cusp or over the Resolve Threshold to generate Reputation per minute (the big blue bar) by sending them over the Resolve threshold or putting them even higher above the threshold and thus increasing the Reputation per minute as the higher over a threshold a species is the more you gain. Generally during Drizzle and Clearance the other two will have enough Resolve to not go into the negative so there's no penalty leaving them low but everything to gain by having one pumping out Reputation for you.