A list of objectives can help you to gauge whether or not your students have achieved everything they should have once the lesson is over. Depending on the subject matter, objectives might be practical, for example, what can the student do at lesson completion. The objectives could also be knowledge based, for example, what does the student know after the lesson is complete.
Lesson plans are great for other settings as well. For example, if you plan on retraining your staff to use a certain piece of software, a plan can help keep them on task and give them a goal to work for each day. This will allow you to incorporate these new lessons into their workday without a significant decrease in their normal jobs. Having a fixed set of tasks to learn also helps employees stay organized and on task.