Spending some time identifying Learning Outcomes can help an instructor or course designer ensure that the course is effective. We will make the assumption that students who enroll in the course have met the pre-requisites, and are academically prepared for the course. If that is not the case, there are additional actions we can take, but that's another topic. Clearly identifying the student learning outcomes helps you develop assessments that measure student learning, so the process is sometimes called "backward design."
The instructor will define the general course goals at the highest level, and then refine them into more specific learning objectives (identifying what needs to be covered, and how) for each course chapter or module. The learning outcomes can be thought of as what the student should know when they have completed an activity or passed the class. For a great explanation and more detail, visit this page.
Your assessments can tell you if the students have grasped the content and achieved the learning outcomes, but only if you ensure that the assessments are aligned with the content. If you test students on something not covered in the course, or if you spend a lot of time on content that is not assessed, you won't know if students were successful.
The key thing about writing good learning objectives is that they need to be measureable. For this reason, we want to avoid terms like "gain appreciation for" or "develop an understanding of" because they are too vague. The attached document has a list of verbs that will help you define better learning objectives. If we think about Bloom's taxonomy, it's easy to write learning objectives for the lower levels (list, define, state), but the most value comes from writing good learning outcomes for the higher levels (compare, critique, design).
If you can write good learning objectives, then you can ensure that the course content covers what you want students to know, and that the assessments measure their learning accurately.