Backdating posts has been a thing on many platforms for quite some time. WordPress allows you to backdate posts and so does Facebook when it comes to pages you Admin.
Why have such a feature? It really just boils down to ethics and or reasoning/purpose. Maybe you missed an important event or birthday you wanted to announce? Maybe you had some sort of drafted post set up and you wanted to publish it on the exact time and date it went live vs it’s actual conception. Least we forget that some users notably use Flarum as a blogging platform and this sort of feature really becomes invaluable to them especially for what it accomplishes 🙂
Overall, thinking about the bigger picture is what it’s all about and if you look at other forum software as well, changing a thread/post date and time is an already core/integrated feature amongst the many forum software out there. Use-case varies from forum Administrator to other forum Administrators in the end.
Let us just sit back and appreciate the time @clarkwinkelmann spent teaching us how 3rd party extensions are developed from an actual experienced developer and all of the new tricks I myself had learned from watching his latest streamed session 😉