This is the default value. The first two blank lines are for the convenience of writing emails. You don't want to always send blank emails to others.

In an email, the signature is just an attachment, not a necessary part. When editing a signature, you can only edit the signature, not the message.

When you write an email, you see the whole email (including sender, recipient, CC, subject, two blank lines (email body area) and signature (of course, if you don't sign, it is blank).