The Moto G5 Plus was designed with a water repellent nano-coating. This unique coating technology helps protect the phone against moderate exposure to water. For example, if you accidentally spill water on your phone or when your phone gets wet in a light rain. It's important to understand that this doesn't make your Moto G5 Plus waterproof nor it can be used underwater. This is a basic water protection. If you submerge the phone in water, you are risking of damaging it. This nano-coating technology is just another layer of protection for phones that has no IP rating and the phone manufacturer wants to add a simple and cheap solution to make it more protected.
I think it's very nice to have this water repellent coating because it happens to almost all of us that we accidentally spill water on our phone. How many of you have been in this situation? I had is many times and in some of those times my phone just stopped working and I had to send it for a phone repairing service and it wasn't cheap. So such a technology can save you the headache of needing to spend a lot of money to repair the device in case your phone accidentally gets wet.
This nano-coating technology helps protect the inner parts of the phone from getting wet and also can prevent corrosion. I personally would have preferred an IP rating of 68 so I can rest assured that even if my Moto G5 Plus falls into the toilet or in the pool it can still survive, but it's not that case. Anyways, it's better than nothing. By the way, I've read that there is even a spray that you can buy that sprays a nanocoating solution which you can use on your phone to protect it against water. I think this is the same idea, but just in this phone it is applied as part of the build process, but not 100% sure.