Characters come in all shapes and sizes.
Some are loving, nurturing care-givers. Others are sarcastic and witty. Still more are the kind of people that if we knew them in real life, we'd want to kill them. Each of them deserves the right to do and act as they should, and that includes using the kind of language that someone like them would use.
People swear. It's a part of who they are, and your characters are no different.
One of the ways to build character depth is with salty language. A reader feels the difference between someone who would say, "Get the f--- over here!" and "Would you come here please?" The emotion conveyed changes with the words you choose for them. Another example is "I really don't like him." and "What a f---ing a--hole!"
They may sound like they mean the same thing, but we all know they don't.
However, just because your character is the kind of guy who would drop an f-bomb with every other word doesn't mean you have to write him that way on every page. Sure, a couple of "language enhancers" sprinkled in there will help your reader show what kind of person he is, but too many will make someone put your book down.
Too many expletives can become a distraction, and the last thing you want is for your readers to lose sight of your story. Some people might even feel attacked or even offended to read such language over and over again in something they picked up to read for enjoyment. Sure, not every reader is going to have a problem with it, but some will. As an author, you need to be aware of that.
I've noticed it myself as a reader. Recently I was reading a book by an author I love, but it was their first leap into a more adult genre. At times it felt like every other word was f-this and f-that mixed in with all of its four letter counterparts, and I found myself rolling my eyes as I read. It became unnecessary, and I was left wondering if the author was doing it simply for shock value.
It wasn't shocking. It was annoying. That author is lucky I like their work enough to even have bothered to finish it.
Season the expletives in when they are needed, but ask yourself if they are really essential to each situation. If they are, then drop that f-bomb like that character deserves. A little jolt to the senses goes a long way with readers. But if it is just salty language for the sake of salty language, tone it down a little bit. The English language has so many wonderful words out there to use. I'm sure you can find a better one.
If you can't, take a deep breath, calm the f--- down, and try again. A better word is out there.