One of my mother favorite phrases was, "Why buy the cow when the milk is so cheap." She often repeated it undoubtedly because she had three daughters. Mom's generation used idioms liberally to express themselves. However, people today are using those same idioms and newer ones are being added to the English language all the time.
Other languages have their own idioms. One of our neighbors was a small Mexican grandmother. What a sweetheart! She was much smaller than I, but she called me mamacita. :^)
She had a favorite phrase, "A woman's work, the donkey eats it." It made perfect sense to me.
You can find a terrific list of idioms at Idiomsite.com. There's even more at Using English.
I use idioms all the time when I talk. Who doesn't? The phrases are repeated over and over. For instance:
Did you get up on the wrong side of the bed?
He's sick as a dog.
I'm going to make a long story short.
Should a writer be liberal in her use of idioms when writing a story? Idioms are cliches--old, hackneyed phrases and many have been around for centuries.
I think it all depends on your characters. Having a character speak a few choice idioms can help round them out--for instance an older woman with three daughters to marry off might use Mom's favorite saying.
Having a character make up their own unique--and funny--idioms would add freshness to a story.
But I don't think all the characters in any one story should be spouting off idiom after idiom. I especially believe avoiding tired old phrases in the narrative of the story is best.
What do you think?