There is a mnemonic that salesmen swear by, ABC - "Always Be Closing". But in fiction, it might be better to say Always Be Continuing. Not only is there often an unnecessary last sentence in a story, there are sometimes unnecessary last sentences even in paragraphs too. Maybe it's a tendency to want "to tie a ribbon on it". But that goes against the need to unfurl, to expand. After all someone could break a tooth on those unpopped kernels of popcorn. When you come to continue writing in your next session, don't you often delete the last sentence from the time before? This is something I'm trying to remember myself, when I try to write fiction.