PRIME is intended for professionals and all-round builds, but then it gets a little weird as ASUS is now pushing TUF GAMING for entry-level gamers and first-time PC builders. As TechPowerUp points out, the new TUF series is pretty strange as it conflicts with how the previous TUF lines were perceived:
The TUF series has until now been attributed to moderately expensive motherboards that are designed with very high durability. They are now relegated to the bottom of ASUS' product-stack, targeted at first-time builders and entry-level gamers. These boards are still built "tough" in that they feature high-grade components, but not as many CPU VRM phases as some of ASUS' more expensive boards.