A consistent style aids the reader. If the punctuation is constantly varying, the reader has to focus on the punctuation and not the message or the prose. And in an ambiguous case, the reader can often rely on the consistent style to help determine what is meant.
As far as house style goes, it’s probably less important for a book publisher to maintain a consistent style among different writers than it is for a magazine, newspaper, journal, or website, where you have pieces by many different writers in close proximity. But for academic presses, it’s really aids the reader to have a consistent style even among different books. It really speeds comprehension to have a single style that is used throughout a number of works.
And when I’ve had my writing professionally copy edited, I’ve found that the a significant percentage of the suggested changes were highly beneficial; the majority were minor improvements, a small number I deemed to be pointless, but went along with them anyway because I didn’t care; and occasionally a suggestion ran counter to what I wanted, and in those cases my will as writer prevailed.