I’m making a specific kind of photo editor designed to redact stuff out of photos. Due to its very nature, it makes a lot of sense from a UX perspective to edit the photo in-place rather than save a copy that the user needs to be aware of (they could mistakenly send the non-redacted original photo to somebody, as they likely wouldn’t see that it wasn’t edited, from the thumbnail alone). Also, not all gallery apps index external app folders by default, so the edited image might not even appear.