Exactly.
Have you ever been frustrated when your boss stops by your desk and asks "Can you just take 5 minutes and do this simple thing for me?" without any regard to all of the other work you have to do, or the fact that the task is really going to take 1-2 hours once you consider all of the nuance and downstream consequences?
This is the same situation. It's a "can't you just..." expectation of the organization without any regard to the other people or the consequences for the rest of the organization.
And like nikisweeting said, it sets a precedent. Once you start granting exceptions for not reading an e-mail to one person, you'd better be prepared to grant that same exception to everyone, otherwise you're going to end up with accusations of unfairness or prejudice very quickly.
Now that you're granting exceptions to everyone, multiply that 30 minute disruption across all of the people in the organization, and then multiply that across all of the different items on your schedule. Before you know it, you're spending half your time working with the people who can follow the rules as a group, and the other half of your time doing 1:1s with the people who would rather match the schedule to their personal convenience because they know doing so doesn't have any negative consequences.