ELI5: Why do people call Zone 3 training (specifically for jogging) "the useless zone" when it comes to building endurance? Do the few bpms separating it from Zone 2 really make such a big difference?

ELI5: Why do people call Zone 3 training (specifically for jogging) "the useless zone" when it comes to building endurance? Do the few bpms separating it from Zone 2 really make such a big difference?