Summary-only ontologies have some undesirable behavior:
Metadata only submission has "(Error Uploaded)" tag displayed next to the submission. That error should not be displayed because there is no file to upload in the first place
BioPortal UI Admin page sets "Ontology has submissions but it is set to summary-only". To my knowledge at least one summary only submission is currently required
ncbo_cron tries to process summary only submissions and errors out for obvious reasons. (ncbo/ncbo_cron#24)
Summary-only ontologies have some undesirable behavior: