There are three reasons for a prophet and apostle (or other leader) working together. The prophet gives vision and direction. The prophet challenges the apostle if they take a wrong turn or go in the wrong direction.
The third reason is more challenging. A key role of the prophet is to protect the people from the apostle. Apostles are dangerous. Most of the people around them have blessed by them or discipled by them, so they tend to look up to the apostle. This means that an apostle is often surrounded by “Yes men”, not because they are devious, but because they love and respect the apostle so much. An apostle needs someone bold enough to challenge them if they are mistaken. That task will usually fall to a prophet. Nathan took this role for David. Barnabas for Paul.
When a prophet colludes with the apostle to attack some of the people, it gets dangerous. When a prophet starts firing the apostle’s bullets, he becomes a pet prophet. This is a risk that all prophets working with an apostle need to guard against.
The prophet gives vision and direction.
The prophet challenges the apostle if they take a wrong turn or go in the wrong direction.