I'm looking at this again and thinking about ways to do it:
1) This could be an account setting that covers all the users in your account, and you can turn on if you commonly enter many events on one day.
2) This could be a user setting that users can change according to their preferences. But this is probably less useful because it's going to depend less on user preferences than on the type of band you have and how you enter events. Also, this would make the replies less predictable because some users would have it on and some off.
3) Or I could add an "auto-digest" function that would be enabled for all users and all accounts. With this approach, request notifications would never be sent immediately. Instead, BandHelper would check periodically for new events, and if more than an hour has passed since an event was added, it would send a digest of new events at that time. This could be the best of both worlds: if you enter a bunch of events at once, they will be bundled together, but if you only enter one event, you won't have to wait until the next daily digest for users to be notified.
BTW for users receiving SMS notifications, it wouldn't be able to show info for multiple events, so it will have to just link to the notifications page in the app.
Also, I'm thinking this would apply to event requests and confirmations, but not event reminders, event updates or set list updates because you'd probably want those to be sent without delay.