If you can no longer afford tuition at your school --- a scholarship falls through, your parents lose their jobs or you can't find a part-time job --- transferring to a less expensive school, such as a community college near your home, is an option. However, according to The Princeton Review, transfer students generally receive less scholarship money than other students, so you should talk with a financial aid adviser at the school to which you want to transfer.
Not all colleges are created equal. Your chosen college may no longer meet your academic needs. You may want to change your major to a program your school doesn't have or the school your interested in has a more renown program. You also may decide to transfer because you dislike a professor or the coursework overwhelms you.
College is more than just a book education, it's a social one as well. It involves roommates, romances and social gatherings. You may choose a well-known party school only to discover you're not comfortable in a constant party scene. Vice versa, you chose an isolated school and want a more active social life. Some students transfer to follow boyfriends or girlfriends. Some even transfer to get away from a roommate they dislike, though it's probably better to change rooms if that's the case.
Family priorities or problems also can cause a transfer. A parent or close family member may become ill so you want to attend a school closer to home. You may become homesick or you might transfer to a school far from home to escape controlling parents.