It's mostly about understanding our solar system and how it formed - comets supposedly contain a lot of early material and could be key to understanding the for

It's mostly about understanding our solar system and how it formed - comets supposedly contain a lot of early material and could be key to understanding the formation of various parts of the system. Some believe that water or other materials from comets were fundamental in the origination of life here on Earth. It also gives us more understanding on the material composition of the rest of space - which might be of more practical use once we start mining space, for example.