While most exercises do not require anything other than an average flexibility, a few exercises call for more than average level of flexibility. Perhaps the most conclusive examples are the squat and deadlift. If you have tight Achilles tendons, hamstrings, thigh adductor muscles, and glutes, for you it will be impossible to squat or deadlift in good form.
In the squat, a person is inflexible in hamstrings, thigh adductors, and glutes, and in this case you will round your lower back as you descend, lean forward excessively, and be in risk of toppling over. Back injuries will be inevitable as soon as you squat with a more serious effort. If your Achilles tendons are tight, your heels will not stay flat on the floor. And if you are inflexible in your shoulders and pectorals you might have trouble holding the bar over your shoulders with clenched hands. Regardless how good or bad your leverages are for squatting, a flexible body will go a long way to make better your squatting form.
Stretching are also of high importance in the matter of flexibility. Developing and then maintaining a flexible body is of great importance. It should become a habit for life. As you become older the stretching are becoming more important becomes. If currently you are tight and inflexible, especially in your lower body, a careful, progressive and systematic stretching routine on alternate days for 4–6 weeks is needed. Only then will you be able to adopt the necessary form in those exercises that demand a higher degree of flexibility.