man 5 newsyslog.d when discussing the size option the text states "...the log file will be trimmed as described above. If this field contains an asterisk(`*'), the log file will not be trimmed based on size." Nothing prior to that statement addresses trimming so it's unclear as to what the asterisk is meant to do. I suspect it was meant to be "rotated" rather than "trimmed". This would read more clearlym, "...the log file will be rotated. If this field contains an asterisk (`*'), the log file will not be rotated based on size."
Sorry - that was sloppy - should be "man 5 newsyslog.conf"