Transport Layer Security (TLS) encrypts data sent over the Internet to ensure that eavesdroppers and hackers are unable to see what you transmit which is particularly useful for private and sensitive information such as passwords, credit card numbers, and personal correspondence. As first step of the communication, TLS creates and handshake between the two machines and this transfer of information is not encrypted. Capturing elements in this packages can reveale informations about the machines involved in the communication.
What is TLS fingerprinting More details on TLS fingerprinting