This question already has an answer here:
Here's an example situation:
I download a file from some server over https, but I also save a "log" of the TLS communication. Later, that file is removed from the server and nobody believes me when I say that the server had once hosted that file. However, the "log" that I saved is verifiable proof that I had obtained the file from the server in question.
I put the word "log" in quotes because I'm not even sure if such a thing is possible. Is it?