Planning helps you to reduce uncertainty or panic and gives you confidence and clarity.
It reminds you to prepare materials beforehand, and makes it easier for you to organize the time and activities flow in classes.
For students, evidence of a plan shows them the teacher has devoted time to thinking about the class.
It is a way to help gain the respect of your students.
It suggests professionalism and commitment.
Planning ensures that the class you are teaching gets a balanced mixture of different materials, content and interaction types.
Planning helps you to develop a personal style.