Zero

It's a great app, no doubt; well designed and functionally responsive. But not all apps need to be everything for all; that is, allow a user to select whether they want an all-in-one or not. Allow the user to select to use the calendar and email feature or just email alone. Is this a big deal? No, it's not.

It's nice to clear the junk out of the inbox and have view options. I've been following this team for a while now; their updates have been well thought out and the app is great.