From this answer I learned that the International Space Station has over 900m3 of pressurized volume. However, the same answer points out that the inhabitable volume is under 400m3. It seems odd to me that so much space is kept pressurized when there's no chance of crew being there, if I understand "inhabitable" correctly.
If these areas are pressurized, what makes them uninhabitable? If these areas are uninhabitable, why are they pressurized?