Every time a new email comes in, you have to spend mental cycles to understand the scope of the email, what needs to be done, who needs to be contacted, what other apps you need to fire up to validate something, and other actions that are likely not directly related to what you are doing or need to do right at the moment the email came in. Scope can vary (your wife is probably not interested in your work calendar, and your manager doesn’t really want to see that you’re taking your kid to soccer practice), but it’s important that in your line of work, people that need to be aware of your work are.