To keep notes, jottings, random thoughts etc. in a place that's easier to modify than a static site but more-open than Notes. Yeah I'm aware of Montaigne but that's only accessible from Notes - not all of my compute is within the Apple ecosystem - but worse it's hosted by someone else.
If building hlte taught me anything it's that giving data you care about to a third party to maintain on your behalf will always end in disapointment. Better never to start in the first place.