What Are The Reasons For Someone Wanting To Be A Library Prefect?

Good question, it seems debatable whether the attraction is job satisfaction unless they are planning a career in the library service.

Far more likely is that a potential library prefect enjoys the peace and quiet, is a book lover and enjoys being around books. Or, possibly, gets a kick out having some measure of power albeit most of the time it will be shushing people and looking stern.

Another possibility is that the person reckons being a library prefect has some fringe benefits. Like impressing those in authority or getting them out of something they don't really fancy doing.

Much more of a long shot is that the person thinks being a library prefect will be good for picking up girls/boys (delete as appropriate). You can decide yourself the likelihood of this idea by observing who hangs around in the library for extra study. Presumably it won't just be geeks and over-achievers.