I have recently had opportunities to work with MODS in creating templates for research and publications data external to the university repository environment.
Multiple note fields can be added each with its own customized display label in MODS. One can add multiple 500 general note fields in MARC but MARC does not recognize a $i display text to differentiate them.
<note displayLabel=”Objectives” />
<note displayLabel=”Background” />
<note displayLabel=”Methodology” />
<note displayLabel=”Progress” />
<note displayLabel=”Implication” />
In the same way displayLabels can be used to distinguish quite different “title” types — e.g. the titles of research program and subprogram as opposed to the title of specific research activity.
And multiple affiliations and addresses can be nested with each personal name in MODS. MARC allows only one — NR (not repeatable) — $u subfield for an affiliation or address in each 100 or 700 field.
Those are TWO HUGE advantages as anyone trying to squeeze nontraditional data into digital archives will appreciate.