I often warn my students that becoming a subject specialist (librarian) is not all glitz and glamour. The idea of being in charge of an entire discipline/subject area for collection is quite appealing (to ~0.0001% of the population, but includes myself). However, purchasing books for your library can be a dream turned nightmare come true.
Consider the following. You are a subject specialist at a pretty ok university and have $40,000 to buy books on political science each year. Yes, this sounds awesome, but it also ventures into a kind of punishment.