
In the old days, when dentistry hurt and cars got about 10 miles to the gallon, Larry Niven carved out a niche for himself by keeping an eye out for interesting developments in science and new models, then incorporating them into his fiction. As he says in Tales of Known Space, if his solar system [Well, he actually says Mars but it can be generalized, I think] seems to be evolving from story to story, it was because it was, as successive space probes expanded our knowledge of the solar system.
A warning: spoilers for stories written in the days of Nixon and Ford follow.
Sometimes this meant his stories immortalized ideas that otherwise fell into the trash bin of history. The idea that the Moon strips air off the Earth and accounts for the difference between Venus and Earth is a Thomas Gold [1] idea that Niven used. The small black holes used in The Hole Man and The Borderland of Sol are courtesy of Robert Forward, as I recall, before Hawking murdered the model on which they were built by showing that small black holes should be very hot. The Hole Man is in particular hurt by this, because the object dropped into Mars should have evaporated its handling mechanism long before, could not
have kept a charge to be handled with and would probably disappear in a poof of extremely energetic particles long before it eats Mars.
I think there's a use for weaponized small black holes. Say you are a large power and there's this planet you want contained to low tech. Now, you're a nice great power and you are not willing to simply kill everyone. On the other hand, budgeting funds for a few centuries of containment does not appeal. What to do?
A billion tonne black hole would be rather toasty and it would stay toasty for a long time, as humans measure things. It also can sail right though a planet like it was not there. If you put it in an orbit that passed through a world, it could keep doing so for a very long time before its orbit decayed below the surface of the world. Gravitational effects would be quite local, and it would not eat the world but what it would do is radiate about 400 megawatts at about one femtometer wavelength or [if it moving at 8 km/s] about 60 kilojoules in gamma rays per meter travelled. Luckily, short stuff like this is rapidly sucked up by the atmosphere. Unluckily, if you are near, this looks a lot like a nuclear device, except that it never turns off and it nukes two spots per orbit, once when its path descends through the surface and once once when it rises out of the surface.
Depending on details of continental distribution and the orbit you pick, it should be possible to arrange things so that every spot on the surface gets intermittently fried on a regular basis. This isn't as inhumane as it sounds, because even 17th century types have the math to predict the path of this beast so they can get out of the way. What it does do is put a cap on the age of the oldest, non-portable structures. No Londons, no New Yorks, no Beijings, or at least not ones that have no been burned to the ground in fairly recent memory. Also no hardwood forests, but hey, eggs and omelets.
1: If you don't know who Gold was, it is worthwhile to google him so you can see what an iconoclast's iconoclast looks like. He could give lessons in scientific unconventionality to Sir Fred Hoyle, which is saying a lot.