They also used to be allowed to simply reject the transaction if you didn't have the money and still charge a $36 fee. It was insanity.
If your checking balance never reaches close to zero, you wouldn't notice this. I was a teenager in 2010 and definitely got hit with a bunch of overdraft fees. Banks know these fees are bullshit (even now, with increased regulation), that's why they're so quick to waive them at first.