When you were younger, were you ever asked (and possibly bribed) to be "friends" with another child who lacked playmates? If you were a new student, did your teacher assign you a "buddy" to help you through the first days? With luck, the arrangements resulted in real friendships. At the very least, you learned your way to your classes without getting lost.
Dorm mates, especially if they're new to school or to the area, sometimes fall into similar roles. They act as co-pilots helping each other navigate the twisting roads of college life, not to mention the actual roads around town. Along the way, they might find shared interests and common concerns.
That kind of relationship is convenient, and can be comforting as well. However, it can also lead to social and emotional static cling. Just because you and a roommate share a food science class doesn't mean she wants to be your partner in your cheese mold project, for instance. Giving a dorm mate a ride to the mall isn't necessarily an invitation to tag along as you shop for jeans.
To foster privacy and personal growth, roommates need to establish individual social and emotional resources apart from each other. Team up with another classmate on that cheese making project. Tactfully encourage a clingy roommate to join a club that fits his or her interests. It's great to spend time together, but some time apart is needed as well.