[456hdsaq234g]

You need a blockchain for decentralised timestamps. That is because a blockchain is basically a slow clock. Its not easy to spoof as you would need to spoof the Proof of Work. Any existing signature relies on a 3rd party trusted clock (like symantecs signing service for Authenticode).

[tylersmith]

In the white paper it's literally called the "timestamp server" and that is its sole function. Timestamping transactions in a decentralized environment.