A literature review places your research in context with historical and contemporary research on a topic. In the sciences, research is part of a huge conversation about the natural world. Doing research without a literature review is like walking into a party and talking without listening to what anyone else has to say. It's polite to listen to what other people are saying and share what you know that is new and interesting to the people in the room. So, don't be a drunk know-it-all in the middle of the scientific conversation. Don't be that guy.