Sociology helps a nurse understand what makes people "thick" the same way psychology does. The only difference is that sociology does it from a "group" or "community" perspective. 
These are important because besides medical knowledge a nurse really needs to be kind, sympathetic and compassionate.
In addition, there are currently many ethical questions in medicine which can be partially covered via the study of sociology. 
Today, nursing goes beyond focusing on disease and pathology  to incorporate a much wider definition of both ill health and personhood 
Nurses are critically involved in making sense and giving purpose to life, illness and death.
Sociology is engaged in the study of human societies. Sociologists are concerned with understanding society in a disciplined way 
Sociology confronts problems which are often subjects of major controversy in society, such as the relationship between social class and illness, the changing role of religion, the rising divorce rate and the changing nature of work. 
Sociological inquiry can illuminate and help make sense of the relationship between private troubles like illness, premature death, and lung cancer and public issues like tobacco advertising. 
Sociology can be of value to nurses to enable them to question the values and beliefs of their professional and the organizational context in which they work. 
We need to understand the social forces which shape and constrain our lives in order to change them.