簡単な回答
Private characters are useful for unfinished cards, personal stories, imported cards that need cleanup, and roleplay ideas the creator does not want indexed or discovered by strangers.
平易な言葉の意味
It is a character for you or your testing workflow, not a public profile for everyone browsing the catalog.
Private-character searches connect creator control, privacy, public discovery quality, and safer publishing workflows.
OnlyKin should keep private drafts central because better private testing creates better public characters.