Citing your sources can be tedious and time-consuming, it's true. But, there are several important reasons why scholars cite their sources, and use a specific format to do it.
It helps if you think of scholarly writing as a conversation. There are certain unspoken rules that we tend to follow in polite conversation, and these make for the best, most memorable, discussions.
Be respectful and give credit where it's due. If you were discussing a topic at a dinner party, you would explain your own opinions and listen respectfully to the opinions of your friends. If one friend made a really good point, you might mention it to another friend the next day. You'd be sure to tell the second friend where you first heard it.
Scholarly communication is similar: experts look carefully at the literature in their field when writing a new book or article, to make sure that their publication fits into their discipline's "conversation." That's the scholarly version of listening respectfully to friends. When they incorporate information or ideas from another article or book into their own writing, they cite it. It's the scholarly version of giving credit.
Giving credit also guards against plagiarism, of course. Read more about plagiarism here.
Demonstrate your knowledge and back up your claims. You don't expect your dinner party friends to magically know things -- if they tell you something amazing, you'll probably ask them where they heard it. Then you'll decide if their source is a good one or not (did they see it on a Facebook meme, or did they hear it on a reputable news program?). Likewise, if your friend is challenging your opinion, you'll probably look up plenty of solid facts and expert opinions to back it up. The more evidence you have, the stronger your point.
Experts do the same thing. They build their knowledge and keep it sharp by constantly reading the publications of other experts. When they publish something new, they demonstrate that knowledge, and support their claims, by citing the relevant sources that they have read. Other experts judge the quality of a new publication, in part, by the quality and thoroughness of those citations.
Share information. If you heard something really astounding at that dinner party, you'd want to learn more. But what if your friend was vague about where he heard it? If he didn't give you enough information, tracking it down later could be difficult (or impossible).
Scholars are curious by nature, so each time they publish, they make sure to provide a path back to each source: a carefully-formatted citation. That way, their readers can look it up and read it for themselves.
Using a specific, standardized format (like APA, Chicago, MLA, etc.) ensures that each citation includes the information that your reader will need to find the source again. Putting each piece of information in a particular order makes the citation easier to understand at a glance (once you're familiar with the style, that is).
That's why citing your sources is time well spent. Luckily, we have some resources that can help you save time when you're formatting your citations! Click here to explore. 
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