Reality shows that you cannot do your research well having materials off-site ... The cost of what you would give up in terms of research, studying, and teaching outweighs the cost of the building.
And the university “thoroughly considered” which works would be out of sight:
They include serial works that have already been digitized, special collections that were not able to be browsed in the first place, and large collections of state documents. Plus, there will still be more than 4 million books in the Regenstein library to be browsed in stacks ... the combination of extensive browsable stacks with high-density, on-site storage as an ideal solution.
In a post at the Wired Underwire blog, “Robots Retrieve Books in University of Chicago’s New, Futuristic Library,” the university librarian says that “research at the university has shown that the more people look to digital resources, the more they consult physical materials as well.”
Here is how the library’s storage and retrieval system works: