As said before, you need a plan to be able to ensure you know exactly what you are going to do to solve something. As if, you did not plan you would be extremely vulnerable to mistakes which can cause problem later on. To go further -- in sciences, you are required to write out a plan, hypothesis, equipment and risk assessment. For example, if you did not write a risk assessment you would be unaware of hazards which mean you would be less safe than you would if you wrote a risk assessment. Hope this helped ;)
