It totally makes sense to have separate libraries even for one project if they can be implemented by different people and tested separately. I'd shout for that design any time of the moon.
Deployment is not the only thing that matters. Development is also important. I am actually working on an interpreter for a web scraping tool, where I'm working on the interpreter and my friend on the IDE. The likelihood of them ever being deployed independently is low but the separation is helping us focus.
