Have you ever heard that a meeting is happening, that you feel you should be attending, but weren't invited to? Have you ever asked someone "could you forward me that meeting?" so that it appears in your calendar?
Well, there's no need to place the action on the other person - with Outlook's side/side calendar view, you can do it yourself.
At the point of "dropping" the meeting, Outlook will prompt if you want to send an Acceptance (just like if you'd opened a meeting request you'd been sent), and you're added to the list of attendees so the originator of the meeting will see that you're now joining them.
So no surprises when you walk into the room.