I have the first-hand experience of not making a paper dummy and getting in a bit of trouble. Luckily, we were able to recognize my mistake just before my project left for the printer. I was able to revise the design and save the client and my company a ton of money. I also learned a valuable lesson that no matter how simple the project may seem, you always make a paper dummy.
This article goes into much greater detail about why spending just a bit of time making a paper dummy is a brilliant move.