There is a school of thought that says that in writing, you shouldn't repeat words. As a result, when you read something authored by someone brought up to believe that, they make liberal use of synonyms.
So, for example, if you read an article about Trump (and that's a good source of amusement), you'll find that the Republican party is often referred to as the GOP.
There's three problems with this. The first is that when I read an article sprinkled with synonyms, I have to pause at each one to translate it. The second is that maybe some people don't know that the term you're using is a synonym, and think that it means something different. But the third is the worst - it's when the writer thinks they're using a synonym, but actually the word has a subtly different meaning, and the reader comes away from the piece with a complete misapprehension of what the writer was trying to say.
Please avoid using unnecessary synonyms. And words that mean the same thing.