In the far future, tiny bots injected into the body can do great good-or great harm, depending on what kind of bots they are.
"...the city was built on many levels, linked by stone bridges. But with the improvements in diet and corresponding increase in stature and strength of the populace, these bridges became too low, and the people would hit their heads. The bridges were eventually done away with in 1764, but the scars on the walls where they once jutted out remain, and in Low Bridge Street there is still one extant bridge, measuring about 6' high." - Chronicler Rasill, Mondopedia, Vol II (The Lands of Hyellia)