Generally put, yoga is a disciplined method utilized for attaining a goal.In this sense, the purpose of yoga depends on the philosophical or theological system with which it is conjugated . Bhakti schools of Vaishnavism combine yoga with devotion to enjoy an eternal presence of Vishnu. In Shaiva theology, yoga is used to unite kundalini with Shiva. Mahabharata defines the purpose of yoga as the experience of Brahman or Ātman pervading all things. In the specific sense of Patanjali's Yoga Sutras, the purpose of yoga is defined as citta-vṛtti-nirodhaḥ (the cessation of the transformation of awareness). In contemporary times, the physical postures of yoga are used to alleviate health problems, reduce stress and make the spine supple. Yoga is also used as a complete exercise program and physical therapy routine.
Source: Wikipedia