If you were unaware, ketamine and similar drugs have been used in humans for their incidental antidepressant effects, which has been getting some level of traction for investigation of late.

Discovering which metabolite was responsible for this in mice is a useful step toward trying said metabolite in humans, since the cognitive effects of attempting some of the things that they did to the mice would be...unpleasant, to say the least, if not outright unethical.

In addition, finding the component responsible will permit them to utilize it as a treatment without any of the concerns , difficulties, or stigma associated with being given an IV of a psychedelic addictive substance periodically.