What's the point of a pen that can take your signature when you sign? Imagine your credit card being stolen, but if the person who's signing gets their fingerprint taken when they sign, you'll have a record of who the thief was. A stupid example for sure, but there are other, more important uses for the device. Some that take advantage of its authentication features:
Chain of custody documentation, Child care and custody records, Patient consent and HIPAA compliance, Sarbanes-Oxley signoff for corporate SEC filings, US Customs Entry and Biometric Passport Authentication
Not really a big deal for everyday use, but for high security situations like handing off a Metal Gear, you want to make sure the guy you're giving it to really is who he is, and not just Snake in a mask.