The first time a Local Population is generated from a Standard Population, its size will change to be approximately three times the size of the original Standard Population. Thereafter, its size will stabilize (unless adding a Scalar Frequency Table which can add between 1MB and 6MB to the size of the Local Population depending on the settings chosen).

The reason for the increase in size is that it:

Keeps a copy of the original Edit List rules
Creates an Edit List that is a merge of the original Edit List rules and the Local Rules
Generates a version of the Edit List that requires no translation at run time.