Can Physiotherapy Help a Lung Patient to Recover From a Chronic Illness?

Can Physiotherapy help a lung patient to recover from a chronic illness?

My son is 6 years old and has suffered a severe bout of lung infection that has caused his lungs to become very weak. The doctors have advised him certain physiotherapy exercises to strengthen his lung muscles. Is it really helpful? He gets very tired after these exercises and I want a second opinion on whether it is really going to benefit him.