I have a soft spot for these darker little details in 'Naruto', so this always stood out to me: Danzo didn’t have multiple Sharingan because he liked collecting weird trophies — he literally grafted them into himself. In the story he scavenged eyes from Uchiha who died (or were incapacitated) and had them implanted into a special, bandaged arm that contained Hashirama cells. Those cells let the transplanted eyes survive and be used as tools. The main practical reason was Izanagi: it’s an ability that lets you rewrite reality for a short moment, but the cost is the permanent blindness of the eye that uses it. If you want to survive fights while cheating fate, one eye isn’t enough.
On a softer level, the flashbacks showing many Sharingan are also storytelling shorthand. They visually communicate Danzo’s paranoia and moral decay — someone who will harvest friends’ eyes to secure power is pretty far gone. Rewatching those scenes, I always feel a mix of disgust and a weird pity: he was trying to shield the village in his own twisted way, but paid for it with his humanity.