Pro Made by a hardware seller
System76 is a hardware company. It configures machines to ship with Linux pre-installed. This means its entire business model centers around delivering a quality desktop Linux experience.
As a result, the company pours more attention onto the desktop. It can fix visual issues and may be able to provide a smoother overall experience than you would have installing a different version of Linux on your machine yourself. Providing Pop!_OS also empowers System76 to make certain fixes for users directly rather than having to coordinate with Canonical or the broader Ubuntu community.
Pro A separate NVIDIA version
Most linux distros seem to hate Nvidia's graphics cards e.g. Fedora and OpenSUSE. System76 have decided to be kind. They have decided to form a good relationship with Nvidia fans and Nvidia itself. By creating a separate installation media that is dedicated for providing support to Nvidia's graphics cards. Even going as far as putting Nvidia's driver updates on Pop!_Shop for users to easily access and install.