Signing out of iMessage on Mac allows you to log out of your Apple ID and stop receiving messages on that device. This can be useful if you are selling or giving away your Mac, or if you want to use a different Apple ID for iMessage.
There are several benefits to signing out of iMessage on Mac. First, it can help to protect your privacy by preventing others from accessing your messages. Second, it can help to free up storage space on your Mac. Third, it can help to resolve issues with iMessage, such as not receiving messages or not being able to send messages.