Digital Fingerprinting is very accurate and returns virtually no false positives.
Heuristics and LexiRules assess the likelihood that an email is spam. They will sometimes block a legitimate email. For example, a marketing newsletter might share some characteristics with a spam email and trigger the rule.
If you find a message in isolation in one of the Anti-Spam Agent queues, you should submit a copy of that message to Websense for review prior to releasing the message from within the Message Center.