Sissy Jupe brings a ray of light and life into the serious and rationalistic world of the Gradgrinds and Coketown. The daughter of circus worker, she represents poetry, imagination, and pleasure. Mr. Gradgrind views circuses as a shameful and ridiculous waste of time and resources. They have no use value in his number-crunching and utilitarian view of the universe—but they are the culture from which this caring girl springs.
Dickens uses the young and innocent Sissy to articulate humane values that treat human beings as individuals rather than numbers. She gets in trouble at school for these views. For example, when she is supposed to be impressed by the reduction in the aggregate number of fatalities in street accidents, she insists on worrying about the grief and suffering of those who still do die. She therefore raises important questions about the utilitarian philosophy of the greatest good for the greatest number. What is good for most people doesn't negate the suffering of the few.
Through Sissy, Dickens points out an alternative perspective to the grim factory and productivity ethos that prevails in Coketown. Love, creativity, and individual human lives matter to Sissy, and since she is a character we like and identify with, we see the wisdom in her worldview.