There are many benefits to e-mail communication over real-time, spoken communication. For one, because the conversation is in writing, there’s a record of what was said, which can be useful both for recollection and to settle any disputes about what might have been committed or agreed to.
Sending an e-mail is often an easier way to organize thoughts than communicating verbally with colleagues and can be a way to convey information to a large group of people at the same time without having to find a time that works for everyone’s schedule to speak to all of them at once in real time.