Pure gimmick. My Bose QC-20s have this feature and every time I've tried to use it, it's been useless.
On planes it's simpler than pausing/removing the headphones to order a drink and the same in the office when you just need a quick yes/no from someone next to you.
There's also a passive mode I use when I'm actually outside with the headphones on. You don't hear engine noise or planes overhead but you can still hear tire noise of nearby cars so you don't get run over. If it's quiet you even hear footsteps.