The newly announced Galaxy S8 and Galaxy S8+ feature 5.8-inch and 6.2-inch dual-edge curved Super AMOLED displays, respectively. Moreover, these QHD+ (2960 x 1440 pixels) displays have an aspect ratio of 18.5:9 compared to 16:9 aspect ratio on previous Galaxy smartphones from Samsung.
It is now being reported that the Galaxy S8 and S8+ displays are set to Full HD+ resolution by default. Samsung moved to a default screen resolution of Full HD on the Galaxy S7 and S7 edge when it released the Android 7.0 update for the smartphones, and it looks like the company will continue with a similar resolution for its newly announced flagship smartphones.
Dropping the resolution to Full HD+ (2220 x 1080 pixels) might decrease the strain on the processor, thereby possibly increasing battery life. However, the screen resolution might change to QHD+ while using the smartphones with the new Gear VR virtual reality headset for sharper visuals.
Of course, you can manually change the screen resolution from the display settings menu to HD+ or QHD+, as per your liking.