They are also a dark matter candidate, though this is more controversial. The ones we are seeing here would be huge ones but their masses could range the spectrum. Smaller ones would have evaporated already but there could be tons of asteroid, moon, and planetary mass ones around.
At least some dark matter may be black holes the size of a hydrogen atom with the mass of an asteroid, and similar objects. These would be incredibly hard to detect. The only way would be their gravitational effects on other bodies or weak anomalous radiation bursts when they rarely encounter matter.
They’re also awesome and weird. One could, for example, shoot right through the Earth. If it was small nothing might happen. Larger ones might cause seismic events or perhaps Tunguska type events due to induced fusion in the atmosphere. What was Tunguska anyway?
The most exciting thing is that if small mass PBHs exist and are common enough, we could find one someday in our solar system, maybe captured as a moon or in an asteroid belt. That would be close enough to send a probe to go look at it and do experiments with it. Being able to directly examine a black hole could be the thing that lets us “finish” physics. It would let us see conditions far beyond anything any imaginable terrestrial accelerator could ever produce.