Of course their role is often to operate as sounding boards or opportunities for the main character to let the reader know how they feel - tell the best friend and tell the reader at the same time - or even as a way to get independent information about the main players - hello two old women gossiping in the hairdresser about the main character.
In my own writing I love the minor characters. My books are riddled with friends, relatives and colleagues of the protagonists. I enjoy creating people who I would like to have in my own life and I especially enjoy writing those fun characters that it's good to spend a few pages with but I wouldn't want around for Christmas dinner each year.
My most recent novel Alphabet Dating features many male characters who only show up for one date - to play gold, see a movie or maybe take in an art gallery.
I don't enjoy books where the characters seem to have existed in a bubble before page one. Everyone has connections in their life, positive or negative, that impact who they are and how they react - a weird neighbour, an office nemesis or a best friend.
Maybe its like real life where I don't like to imagine anyone sitting alone on their birthday I like characters who have full lives. I don't mind if they're running away from the mob, falling in love or facing the zombie apocalypse I would like to think someone was worrying about how it turned out for them.
What about you? How important are minor characters to you in fiction?
Alphabet Dating is available on Amazon