Molière, a french playwright of the 17th century (1622–1673) wrote a well known comedy ballet called “the bourgeois gentilhomme”. Monsieur Jourdain, a French bourgeois, wants to become a gentleman. He hires a coach to educate him in the good manners of gentlemen. The teacher decides to teach him how to speak in “prose”. And what Mr.Jourdain discovers is that prose is the same language he has been using since he can talk.
The answer to your question is similar to this story. You have been making your supply chain work satisfactorily since the beginning. Your products are of high quality and your customers are happy. You have been speaking native supply chain since the beginning. Why bother with a supply chain and logistics department?
Start to worry when your customers become unhappy or your costs to keep them happy outweigh the benefit.