In order to help save battery life, a new feature Samsung introduced a new scaling option in the Galaxy S7 and S7 edge with the Android Nougat update. You can now choose to set your display to either WQHD (2,560 x 1,440), Full HD (1,920 x 1,080), or HD (1,280 x 720). What happens when you update is it defaults to Full HD. It won’t be that much of a different experience but if you crave having a higher resolution screen, you can easily change that back. Simply head to Settings > Display.
Source: Android Central