Lesson planning is an integral part of the instructional cycle because aside from it being required, this will serve as a guide to the teachers and make the teaching process more organized and effective. You cannot just teach students without planning a lesson because you have to consider a lot of things. You have to make sure that everything is aligned. From learning outcomes, to discussion, until assessing students.
A lesson plan is a written curriculum in minuscule. Learning outcomes, subject matter, teaching-learning strategies, and evaluation are necessary part of writing a lesson plan. All of these parts should be aligned so that at the end of the teaching-learning process, learning will be achieved.