Thoughts on using dialogue for characterization?

I read in a book about writing that dialogue should never ever ever be used to convey a character's personality. Is this a common rule? I personally hate it in books when characters only ever speak to move the plot forward. It makes them feel like unfeeling robots and I can't picture them as real people.

Is it just me or does this rule seem really dumb?

Edit to Add: The book is "Novelist's boot camp: 101 ways to take your book from boring to best seller"by Todd Stone

Quote:

"For example, you'll learn that you don't use dialogue for the sole purpose of showing the reader some aspect of a character's personality or for revealing backstory... your characters should use words as tools or weapons to fight for and get what they want, both within a given scene and within the overall story" (pg 11)