You want your writing to be easy to read. Readers enjoy reading material that is easy to read. Material that is hard to read makes them bored or annoyed. They may miss the point you are making. You don’t want that.
There are lots of things you need to do to make sure your writing is easy to read, and one of them is being consistent. It’s not boring to consistently use the same term for something you refer to throughout your writing—it’s helpful. It’s also helpful to use the same heading styles throughout your document, and to use the same citation format throughout. Yes these things are tedious to pay attention to, but using your software tools can help you a lot with these: for example, using styles in Word and reference managers like Endnote.
These are just some examples of the consistency needed in your writing and Geoff Hart talks about some more in this short blog post.
Hart, G. (2012) Five ways that consistency matters. http://intelligentediting.com/resources/five-ways-that-consistency-matters/