What is the advantage of using verified mail address and domain?

I was trying Amazon AWS SES which is working great right now. The thing is I can send e-mails without filling in the verified e-mail address and domain. What is the advantage of using these two fields? Is it just for the ISP to verify if the e-mail is spam or not or is there more?

And what does "domain" mean anyway (conjunction with SES). Is it to verify custom mail addresses like the "test" domain in someone@test.com ?