i upload unlisted videos to share privately with a single family member. or as a backup so i dont have to store it on my phone etc. silly to assume that people post things because they want it to be seen by e v e r y o n e.
i cannot speak to the current situation, but years and years ago, it was a thing. i had a crappy motorola razr smartphone in like 2012 that i set up dualboot on, and i think i also had dualboot on my google nexus 5, though i could be mistaken about that. it was a thing though.