I can still see my dear Senior English teacher standing before us looking over her nose tipped glasses.
“The correct usage is ‘The book THAT I read’ not ‘The book I read.’ That instruction is probably ingrained in my DNA. Her excellent teaching writes every book right along with me, but in modern fiction, it isn’t necessary.
Thank heaven for the ‘Find’ feature in my word processing program. I tend to use THAT in sentences where it can easily be omitted without changing the meaning.
The word "that" is overused and rarely necessary except in the definitive sense. "What car?" "That car." "What car did you drive today?" "The same car ["that" is implied] I drove yesterday.”
In our quest to slash anything that doesn’t move the story forward, add the unnecessary use of the word THAT to the list.