The Samsung Galaxy S8 Plus features a 18:9 aspect ratio display allows Samsung to create a phone that comes with a larger display and is still comfortable to hold in your hands. The Samsung Galaxy S8+ has very slim bezels but it's not bezeless as some sites mention on their websites. This is the same approach that LG used with its LG G6 smartphone.
Here is a leaked video that showcase the Galaxy S8 and the S8+. You can see that the phone is somewhat narrower, at least judging by the person's hand in the video relative to the phone's size.
In the future we are going to see more and more vendors starting to use this 18:9 aspect ratio, as more 18:9 content becomes available for this unique viewing format, because it's more comfortable to operate in one hand and because the extra vertical space can be used to add extra functionality and improve the way users interact with the user interface. LG has implemented it beautifully with some really great features that take advantage of that additional vertical space. It's definitely better than having an screen-edge or second-screen functionality, which is in my opinion very cumbersome.
At the end of the day, this screen allows Samsung to provide its S8+ users with improved one-handed usability, a great viewing experience and offer then with some unique and productive UI features. In the future, this type of display will become a standard, but it will take some time until we'll get to see content that is optimized for this specific aspect-ratio. With the LG G6 we already saw Imangi Studios updating its Temple Run 2 to support the 18:9 aspect ratio. This is just one game that has support for it and in the future many more game developers and content creators will create content for this particular type of display. When you buy the Samsung Galaxy S8 Plus, you know it's future proof, and if 18:9 content comes along, you know you will be able to enjoy it.