It means you can more accurately trust messages as coming from bitcointalk.
Meaning, you don't need to be afraid of phishing, if SPF or DKIM comes through, you know the message is genuine.
It might not be that important because the forum rarely sends notifications to users via email. There is an option in the settings under Notifications and Email , "Receive forum announcements and important notifications by email". That is ticked in the user's profile by default but I don't remember ever receiving any notifications. Meaning, you don't need to be afraid of phishing, if SPF or DKIM comes through, you know the message is genuine.
You can opt in to receive email notifications for threads that you follow, but the old rule of not clicking on links in emails should still be respected even if those mails are from Bitcointalk.
On an unrelated note, I am always glad to see something written in Swedish, even though it's just a screenshot.
