What's this new button in Storyline?

I have recently updated to the latest version of storyline. I'm not a fan of some of the changes such as the copy/paste triggers being altered in such a way that it is now more efficient to just start each trigger from scratch. But I cannot figure out what the 'person' icon in the timeline is for

I have clicked it on and off and it hasn't changed anything, and there is no hover text for it so I'm a little stumped. Can anyone enlighten me please?