In the case where no capacitance is specified for an instance, the instance will "inherit" the 100 pF value from its definition. A value specified will "override" the value on the definition. If a great number of attributes end up being the same as on the definition, a great amount of information can be "inherited", and not have to be redundantly specified in the netlist, saving space, and making the design easier to read by both machines and people.