In The Boss Baby 2017, the baby says "Cookies are for closers". There are many references of the expression and few video clips mentioned it. I cannot tell from the results if they deal with the meaning of the phrase.
It is a humorous reference to the David Mamet play "Glengarry Glen Ross", which is about unscrupulous real estate salesmen worried about losing their jobs. At the start of the play, the salesmen are harangued by an abusive "motivational" speaker visiting their offices. When the salesman who has failed to close any recent deals tries to get a cup of coffee from the office's machine during the monologue, the speaker shouts, "Put that coffee down! Coffee is for closers!"