It’s a fair question. A variety of people read your writing. Why would you alienate some by using certain words? What’s the purpose? It goes along with one of the ten cardinal rules for writing: Use Dialect Sparingly. What does that mean?
First, certain people use the f-word and others don’t. In Redemption Sam Johnson uses it with some frequency. He also has a certain dialect. However, Sam has just spent 17 years in prison for a crime he didn’t commit. If you had spent that much time in prison, you might say F**K too. As Kurt Vonnegut said, “My characters speak coarsely because people in real life speak coarsely.” However, if your character is a Harvard educated librarian, and she uses the f-bomb outside of extraordinary circumstances because you want to shock your reader, delete that scene and start over. Only use such words realistically.
Don’t overuse the salt. Dialect and cuss words are like salt in the pages of a book. Some adds flavor, and too much ruins the plot. Your characters don’t have to speak proper grammar all of the time in dialogue and it’s okay if they cuss. But don’t turn your reader off by overusing it to the point where they are tired of it. Foul language has gained more acceptance in modern fiction, however moderation is the key.
Suspend disbelief. Your job as an author is to make me believe, just for a little while, that what you say is happening in your book is really happening. You want it to play like a movie in my skull. You want me anxious to see the next scene, to long for the finish, not dread the next time your character opens his mouth. This is a tough lesson to learn, and if I could have some of my young writing back, I would likely do some things differently.
What’s the answer then? Use the f-word or any other cuss words like dialect or salt in a soup. Don’t overuse them. Do use the f-word for sailors and prisoners, don’t use it for librarians and old maids. Think about your reader. Is this believable? Will they forgive your use of the word here even if they don’t like it because it feels real? If you can answer “yes” you’re probably on the right track.