This is important not just because it guarantees the trainer will understand the materials. It’s because doing so increases their knowledge of the materials and prepares them for any skepticism met in its presentation.
The process of creating course materials for a workshop deepens one’s knowledge of the materials. It also has the author question the assertions made. Good materials are conveyed in a particular order for a particular reason – it is important to understand this. Without this deep knowledge mostly only information can be conveyed. Creating materials also involves anticipating questions and skepticism of what is being taught. This process literally gives deeper experience to the instructor.
The recent trend for certifying bodies to bring in outside trainers to create materials for them is good in many ways. But it also means that these companies are becoming somewhat more about marketing than about creating new concepts. They are taking other people’s work and putting it into their marketing and delivery channels – having trainers who don’t have the experience to build such a course deliver it.