Because there are bad colleges and universities - yes, even in Sunny San Diego - the public wants to know that there are ways to separate the wheat from the chaff. In this situation, low-hanging fruit in the performance evaluation process are student evaluations. At more and more institutions of higher learning, student evaluation scores have therefore grown in importance to the point where they may even determine singlehandedly an instructors' continued employment.

Some people may say, "So what? Great, fire the shmucks, who can't get good scores from the students!"

Of course, this view leads to problems. Having worked for multiple private schools, where student evaluations are overemphasized, these are the consequences I have seen from this overemphasis, each to varying degrees,  depending on the institution and its management priorities and skills:
 

• Grade inflation, sometimes massive: students, who get  'A's rarely write negative evaluations, so instructors who want "good evals" simply "grade easy."  Of course, this destroys academic integrity and the viability of the program itself, given that graduates will not find or keep jobs without competitive skills: short-term gain (good grade) for long-term pain (no job, no income).
• Dumbing down of the curriculum: same problems and results as the previous scenario.
• When students believe that they can fire an instructor (with their evaluations), quality of instruction is doomed, as the professor is now hostage to student whims and demands.
• Turnover and poor instruction: good instructors/professors will not subject themselves to the unfairness of this system - after all, most students are not qualified to professionally assess the quality of instruction provided by a teacher. This leaves mediocre instructors, who cannot find other work.
• More general process and quality problems: an institution that fails to establish educational, instructional, and pedagogic best practices coupled with meaningful fair, and consistent evaluation far beyond simplistic student surveys will also have other problems, most of which eventually lead to stagnation or even failure. This is why best-of-class universities grow rapidly, and mediocre ones subsist, at best.
• (Of course, even worse, when institutions pay attention to the willful posts by anonymous students, often disgruntled or vindictive, on sites like RateMyProfessor, they only prove that they lack proper professional assessment processes and practices.)

What is needed is a fair comprehensive evaluation of real instructional performance. With a focus on student learning outcomes and subsequent student success, a high-quality, high-yield evaluation process will inform school management about its instructors' best practices, and what areas need constructive improvement.  Well-constructed, statistically scrutinized student satisfaction surveys collected across multiple classes and periods can provide one perspective into a teacher's performance, but should never be weighed as heavily as peer evaluation and other fair methods.

No school that uses student evaluations as primary or only instruction quality measure should be accredited or retain its accreditation.

Using student evaluation scores to threaten instructor termination (overtly or as a rumor) is never fair or equitable and damages the school's reputation with all its stakeholders.