The basics for deciding how detailed a guide should be has to do with the key parameter of scalability. For example — does your program need to be delivered many times to many people and perhaps in many locations? If so, more detail and structure will be needed. This is because, as we turn a program over to someone else to deliver, we are transferring control.
The instructor and the course developer are one and the same. In other words, you created the program and you are the only one that will teach the program. You will need great participant materials, engaging activities, and visuals that support and illustrate concepts and key points. The instructor/facilitator guide, however, may just be a simple outline showing the sequence of instructional events with notes to remind yourself of timing and student references. After all, you wrote the program, so you would know what you want to say and do.
One or more of the course developers will deliver - but others may be selected and trained to deliver the courses and will then be on their own to deliver the course. Now, not only will the materials that the students use and see need to be complete and sharp, but the instructor/ facilitator's guide will have to be much more detailed to assure reliability. That is, the program will be delivered in such a way as to attain the same results and provide a very similar experience regardless of which instructor is delivering the course.
Other instructors/facilitators will deliver the program, but you may not be involved in selecting them or training them to deliver the program. In other words, you design the program, then test it out, and then send it out to the world - sometimes as an entirely self-contained program. In this case, as you have lost much more control over presenter selection, each presenter acts more as a facilitator, using the carefully scripted guide you have developed. In a level 3 guide, the content is mostly contained in the student materials.