According to the Gabrielle dictionar, an anecdote is a personal story used for a purpose. These are used in articles and essays nonstop 24/7 all the time but since this is the Incredible Writing Workshop we're talking about fiction and poetry.
Anecdotes are awesome when you write a novel,because if you're completely stuck and have no idea which direction forward is, you can employ the Storyteller-Like Character and have him/her tell an anecdote. Old Uncle Joe or Little Cousin Tashika can serve this purpose well.
I love when authors use anecdote-telling with irony, like when the weird old woman starts talking about her dead boyfriend and the Protagonist doesn't pay attention... only to discover that the Antagonist is the dead boyfriend's great-grandson!
Anecdotes have obvious humor purposes in
fiction, because what happens to us in life is often funny. Think Mark Twain. Show the tension of a short story when the Sibling launches into a raucous tale of the Protagonist as the Prot. stares helplessly at his Dearly Beloved. It's funny, gives background and moves the story ahead all at the same time.
In poetry, anecdotes can help us remember the feelings
that moved us. Are you writing a poem about embarrassment? Write down the full story of your Most Embarrassing Moment (then burn it. I've never told my MEM to anybody. It's too humiliating.) Underline the phrases that give color to the story or express the events succinctly. Look for odd noun/adjective combinations, and begin to shape your poem.