Floo powder requires a fireplace connected to the Ministry-supervised system. It’s meant to be secure enough that it can connect locations where wards would prevent you from just Apparating there (like people’s homes and Hogwarts) Apparation requires being an licenced wizard and (in HPMoR atleast) you can only visit places where you’ve already been. Portkeys can take you to new locations, and only need expertise in their creation, not their usage, but each portkey can only take you to a specific location.
The above are differences enough that you can see why different forms of transportation would be preferable under different scenarios.
Floo powder requires a fireplace connected to the Ministry-supervised system. It’s meant to be secure enough that it can connect locations where wards would prevent you from just Apparating there (like people’s homes and Hogwarts)
Apparation requires being an licenced wizard and (in HPMoR atleast) you can only visit places where you’ve already been.
Portkeys can take you to new locations, and only need expertise in their creation, not their usage, but each portkey can only take you to a specific location.
The above are differences enough that you can see why different forms of transportation would be preferable under different scenarios.