When you’re sending an email with an attachment, do you zip the attachment?
Have you ever sent a document to someone only to find out that the document the recieved, won’t open, or doesn’t look right?
Email itself is very prone to having it’s attachments corrupted. By zipping a document, not only do you shrink the size of the document to be sent, but you are also encasing it in a way that prevents tampering with the data itself.
By shrinking the size of the document you are lessing the chance of corruption by sheer ratio.