It's all about finding the most efficient order to get things done. A better order can make a huge difference.
The rover is needed for the late game, once you've already established a camp and a steady supply of supplies. Then the goal is to maximize your mission rating.
The rover is necessary to transport crew members to a specific location to complete certain tasks. To find the points of interest, the drone is very useful because it is faster than the rover. But you can use both to unveil the map.
To use the rover or drone, you need at least one person to fly or pilot it (seat 1). Some tasks require a person with specific skills at one location, but it is recommended to have a pilot to drive or fly. So in this case, it's better to send two people with the rover (pilot + specialist).