If there is any chance that you will be near the ocean, a lake, a bathtub, a glass of water, or ANY body of liquid, yes. These cameras on their own are quite an investment and it is worth the extra bit of money to protect them. Not only does a waterproof case protect the camera from water, but it also provides shock absorption if you drop the camera. There are some cameras that are innately waterproof, but not all.
Even with GoPros, the waterproofness varies model by model. When choosing which waterproof case to invest in, be sure to look at how the case is attached, if you can still access all of the buttons, and the customer reviews. In the reviews, you will learn a lot about the ease of use and durability of the case. If you want to play it safe, it is also a good idea to buy a case that is made by the same manufacturer as your camera. This way you have no doubts about if it will fit properly and button access.