ETFbitcoin:
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.
I see, i know it's roughly about authentication, but didn't know about the implication.
However, some mail client doesn't show whether the mail has SPF/DKIM and you need to see the header to know whether it's exist or not. Additionally, most users usually rely on spam filter and human-friendly warning message shown by mail client (e.g. "This message seems dangerous" on GMail).