The expression used to generate default values for a field on the postgres database are currently being printed on the feature form.
nextval('serial')
A new option in the "project properties" (tab "Data Sources") allows evaluating the expression before opening the form and will directly print the new value in the feature form.
23
The main advantage of this improvement, is that one can now directly create and link records of related tables before having to save the data first, because the primary key is already present before the feature is saved.