"Tor is free software and an open network that helps you defend against traffic analysis, a form of network surveillance that threatens personal freedom and privacy, confidential business activities and relationships, and state security."
In other words TOR works much like the Open Proxies, however it's mostly used by legitimate visitors who just want to remain anonymous in Internet. Note that it can be abused by malicious visitors. Also note that if they wish so, they can visit your website with their real identity without TOR. In any way, TOR detection is disabled by default and it should be disabled unless you have specifc reasons to enable it.
In order for the TOR Project Detection to work you have to enable the TOR Project Detection option in your Settings.