By being able to examine microscopic details, knowledge has been extended. That knowledge has been put to good use. An understanding of certain types of diseases, for instance, resulted from the knowledge about bacteria that microscopes provided. Knowledge can also be put to undesirable use, as in the development of bacteriological warfare. Using microscopes shows students that things exist that cannot be seen with the naked eye.
Microscopes have limitations.
A light microscope can not resolve detail smaller than the wavelength of light. Other technologies have been developed to view smaller things, such as some kinds of viruses. An interesting project that some gifted students might undertake is to photograph objects through a microscope. This is a rather specialized field of photography, requiring high resolution film, and a special microscope adapter to fit a 35 mm camera. The slides or prints obtained can be used to enhance science fair projects, or kept from one year to the next to build a collection of specimens.