[bluGill]

Many buildings are designed that way. It is a useful thing to do, but there are trade offs - you pay for that extra space in other materials and extra time. For an office the office/cubes/open layout is installed by the renters after they lease the building and thus the space you are talking about isn't part of the initial construction effort. They still plan/reserve space for the pipes and large wires in initial construction. Generally the bathrooms and break rooms (kitchens/cafeteria) would be done in initial construction and so carefully planned out.

It of course isn't illegal to make changes - but it is expensive and thus not something you should do. (though some things are much easier than others to retrofit half way in.