This function is especially useful for groups that work on the principle that all members are expected to attend events and only reply if attendance is negative. Examples are: Multiple classes in a sequence, Golf league or team sports events.
A very important related capability would be simplification of registering a group of members to a group of events - either manually selected or by member type.
I run a beginner's mentoring golf league to assist women in learning golf to establish business and professional relationships. Our golf league is set up for multiple sequential sessions of 8 weeks each. Members types are used to specify which sessions the members pay for. Then, within a session, each week is a different event - with separate reminder emails and attendance. The default behavior is that members attend all 8 weeks, but sometimes they have to cancel due to work commitments.
I have tried for two years to get members to sign up for each week. Every session, most new members just don't understand they have to do this, and I end up registering them after a number of email exchanges where the new member is embarrassed. It is very time consuming to sign 30 members up for 8 events multiple times through-out the year. Some members have been trained and do the cumbersome process themselves. Most experienced members just send me an email saying: Sign me up for all except June 10th - so I end up doing most of the registrations thru 3+ pages per person per event.
Also, our current policy for cancellation is to send me an email and I manually delete the registration. Allowing a member to cancel a free registration would be very useful.