Microbots are designed to work INSIDE the human body, doing things you can only do when you are right there, at the site of the problem. What kind of problems? Busting up blood clots or plaque along the arteries. Taking bits of tissue from a tumor on your liver and, better yet, delivering drugs to that tumor to kill it without exposing surrounding cells. Microbots are being developed and tested for these and many other on site tasks inside the body. Does this remind you of the Fantastic Voyage*? The future is HERE.
*Fantastic Voyage was a film about the Proteus and its crew, who were shrunken and then launched into the blood of a scientist who they needed to save. See trailers here.