It is a normal human tendency to organize information into nice neat categories. These generalizations or stereotypes are damaging if we limit information or experiences so that they fit into our existing categories. Almost all students report that things weren't at all what they imagined. Stereotyping works both ways. Just as we tend to have stereotypes or limited information about people and places we've never been before, others will have similarly limited ideas about us.
Stereotypes can be negative or positive.
For example, North Americans are often characterized as being highly independent, competitive, practical, and generous. These can be seen as positive traits. However, the same traits can also be seen from a negative perspective - that North Americans are only concerned about themselves or money, are incapable of appreciating the intangibles in life, and are too innocent or naive. Women might not have the same status or role in the host country that they enjoy at home. Consequently, they could find themselves in situations where they experience anxiety, confusion, fear, powerlessness or anger.