You look at your calendar and you see that you have meetings all day. For those meetings you invited, you want to quickly know whether the majority of the invitees have accepted, declined or need to be reminded as of no response. Based on this overview, you quicker see whether you need to take action, e.g. reschedule the meeting to a different time or remind people to respond.
The idea is simple: In the calendar view, add a small color line to the bottom of the calendar entry, symbolising the percentage of participants who accepted the invite (green), no response (grey/yelllow) and who declined. All of a sudden, your calendar tells you even more information about your meetings at a glance.
BTW: IBM has a patent on this