Reduces damage you take. It's arguably the least practical stat to enhance.
Unless you do a EV/BL combo to make him as invincible as possible from evading and reducing damage of normal and skill attacks. But usually this would only be most useful and deadly if you even manage to reach BM.
Would work better if it's put on a QA Digimon (due to larger EV% boost) with some DE plates and spam skills away.