Minimum use of disk space: when you perform a calculation or another operation and the outcome is a dependent map or table, in principle only the object definition file of the dependent map (.MPR, .MPA, .MPS, .MPP) or table (.TBT) is stored on disk. Object definition files are small ASCII files and they store amongst others the expression by which the output object is created and contain a reference to the output data file(s). You can directly continue to perform calculations and/or operations on the dependent objects that do not have calculated data files yet.