Another reason is that accreditation confers a degree of legitimacy. A degree from a non-accredited college is cause for suspicion in the minds of many employers.

Now, the colleges that don’t bother with accreditation fall mostly into two categories. One is the legitimate special interest colleges, usually affiliated with a religious denomination that objects to secular oversight of any sort. The other is the fake-o diploma mills that will give you the PhD in quantum astrophysics in two weeks with no coursework or exams for just a few thousand dollars.

Many schools are concerned about their ratings in such publications as US News and World Report. Accreditations (or lack thereof) are likely to be part of the criteria used to judge a school’s quality.

On a more professional level, colleges like to know that they are meeting at least minimum standards. Also, sometimes, a particular group of faculty–e.g. business, education, etc.–will use an upcoming accreditation to get their university to spend money hiring new faculty or improving facilities.