Usually, if you want to send someone an email, you are supposed to know the email address, but that’s not always the case. Many sites use contact forms and now it’s very easy to create one added a contact form, but it was disabled by default. Google+ made it easy to send someone a message: just add “+”, mention his name and he will probably receive a notification, depending on his notification settings.
Now you can send email to the people from your Google+ circles even if you don’t have their email addresses. Gmail will show suggestions from your Google+ circles when you compose an email and will send your email without showing you the address. “Your email address isn’t visible to a Google+ connection unless you send that person an email, and likewise, that person’s email address isn’t visible to you unless they send you an email.“