The Romans put great emphasis on realism in their art. Representations of people were created to express who they really were even while showing their imperfections. This was different from the Greeks who mainly displayed people in a form that was as perfect as possible. The Greeks were not interested in realistic representations for the most part, but in faultlessness. The Romans seemed to be all about recreating people as they really were, not just in an ideal format.
Why was verism so important to Romans? I think one of the reason it was so important is because it was an expression of their culture. It was their own unique style and gave them distinction from the Greeks. It could also be that they wanted to present their culture in the realest way possible. Making perfect images does not necessarily show "who" your culture is, it merely expresses the idea of what you want your culture to be. Showing people for who they actually were could, arguably, give a better feel for how the Roman culture actually was. With these things in mind, Roman artists could express the traditions of Roman society while developing skills in art and growing in new approaches. They were able to create realistic pieces that contained important elements of the people and objects they were creating. Because of the Roman fascination with verism, we are able to get a glimpse into their society. We can see a statue or a painting that represents a human being, and not just the "ideal" description of them, but their actual self. This is the legacy Roman art left.