The body has a natural alignment that helps it move efficiently. When bones are stacked on top of each other in the most efficient way, the muscles and joints of the body react evenly to the force of gravity. This is evident when standing or sitting, but it is also present when in other positions, for example the poses of Yoga. It also comes into play when moving through space in any physical activity such as sports, dance or even playing a musical instrument. Also workers who do not have ergonomically designed work-spaces will be familiar with the aches and pains of being in misaligned positions for long periods of time.
Alignment helps the body move in the most efficient way to reduce strain on joints and muscles. Being aligned also helps the body to use energy in the most efficient way. Tense muscles use a lot of energy by 'holding on'. The body is always trying to bring itself back into balance, so when there is continuous misaligned pressure on bones, joints and muscles the body develops tension because it cannot rest in an efficient way.
Becoming aware of imbalances in the body is the first step to gaining efficient alignment, then you can improve strength or relax muscles to help bring yourself back into balance. Any somatic based practice will help you become aware of your personal misalignments but it will also help you recognise what is balance for you. Your body is unique to you, so it is a process of fining what feels good, natural and efficient for you.
Alignment is dynamic and not a static state so it's also important not to beat up on yourself for any misalignments that you become aware of. The body is misaligned naturally many times throughout the day, what's important is to recognise this and to release any unhelpful habits of remaining in these positions so that the body can easily find it's way back to balance.