Google Calendar's new Optional attendees feature lets meeting creators communicate how important your attendance is at a meeting in a couple of clicks.
Guests' roles in meetings tend to vary as well. Some people have to be there to lead the meeting or help make decisions, whereas others are gathering information they may be able to digest just as well via the notes. Without knowing which attendees are crucial and which are optional, it can be difficult to know which meetings you really need to attend.
That's where Google Calendar's new "Optional attendees" feature comes in.
When you're creating a guest list on a new event, you'll notice a new "Make some attendees optional" link above the guest list. Click it, then click on the bust icon next to each person to toggle their attendance priority.
Optional attendees in Google Calendar [Official Gmail Blog]