Many simple lifeforms see our body as a plentiful sack of resources -- bacteria desire our proteins, carbohydrates, and iron and viruses seek to turn our cells into viral factories. Since these thefts hurt us and can even kill us, we have developed immune systems that destroy these on "sight," along with malfunctioning cells a la cancer.
While our immune system is strong, we benefit from helping it out, especiallyin medical situations where all tools must be absolutely sterile. Our existing plans for this involve high pressure steam, which heats the tool to temperatures that denature the bacteria and virus's proteins so that they cannot survive. We also have chemical attacks such as alcohols that have the same effect. This is also required to a lesser degree in other fields like restaurants, in which it would be bad if a client caught a disease from another.
Suppose one made a nanobot that dismantles known bacteria and viral proteins and uses them as raw materials to make additional nanobots. If one kept tools in this environment, the tool would stay sterile for cheap. (Presumably there is a means to prevent the nanobots from escaping, such as requiring them to stay within a power field not provided outside the toolbox.) In addition, if these nanobots could be taught not to attack human cells, and could be powered in a human body, then this would restore immune function to the immunocompromised. This would greatly increase their quality of life. In addition, immunocompromising diseases attack immune cells through attachments to their cell membrane. These nano-immune system devices do not have one of those.