The use of end-to-end encryption lets you hide the content of your message, that you sent a message to a certain person (or received one from them) will be apparent. The server can’t read the messages, but it is definitely aware that you exchanged messages on a certain day and at a certain time. In some cases, merely communicating with particular people may draw unwanted attention. If someone gains access to the device you use to communicate, they will be able to read all of your messages, as well as write and send messages on your behalf. Therefore, protecting end-to-end encryption requires the protection of devices and application access even if only with a PIN code so that if the device is lost or stolen, your correspondence, along with the ability to impersonate you, does not fall into the wrong hands.