Without instructional design, a course can lack structure, have poor navigation, and have issues mistakes due to not being evaluated. It is important that the course content matches the learning objectives and encourages student participation. 

While in school, I've experienced many types of lectures but I never learned about them from a curriculum or instructional design standpoint. I think it's a good rule of thumb to engage students by not having every lecture be expository, especially in an online class. The other types of lectures involve more student centric learning.

There are benefit to Synchronous and Asynchronous courses. Asynchronous allows courses to be completed at a learner's own pace, and is more learner centric. Synchronous courses can be more engaging, while allowing for guest lectures, and students interacting in real time.

Without structure, an online class will not be successful as students need to know what to accomplish in order to do well in the class. It should be the online class should be easy to navigate so that students can learn and complete all the requirements.