Once a MendixObject is retrieved from the database/created, this value is set (id defaultvalue or the value it got from the database)

Thus, once you start changing values in microflows, java actions etc, this value will remain the same until you commit it (in which case, the next time you call this method, it will return that value). It's sometimes used to keep track of everything that's changed, so that people can keep logs containing the diffs.