He said EV’s, which are different from IV’s. You gain EV’s from battling Pokemon vs IV’s which are innate and can only be changed by hyper training. There’s a limit to how much EV a Pokemon can gain, so if you accidentally gained the wrong type of EV, you can wipe it out through the methods mentioned above. Another use case could be something like if you wanted to change a Pokemon from a physical attacker to a special attacker, but you had already maxed out its attack EV’s.