I found the following in the Hindupedia and have summarized it because it is an interesting perspective on why we perform yagyas, and what we can expect the results to be.
<<Agni (the god of fire) is called the face of all gods and is central to the performance of yagya. Oblations of wood and ghee and occasionally other items, are offered into the fire. The yagya offerings are the food of the gods, and in return they support our own desires and promote the well being of all through rain (as told in the Bhagavad Gita).
All of life is said to be a yagya. Every action, when made as an offering to God is a yagya. Actions performed not so much for material gain, but with a selfless motive, is the highest form of yagya. Sacrifice brings transcendence, and transcendence is the ultimate meaning and goal of life in the vedic system.
In the vedic system there are two directions in life; pravritti and nivritti. Pravritti is the process of accumulating and indulging in desires and wishes in a worldly sense. Nivritti is the process of clearing away karmic debts and developing a transcendent consciousness. In terms of pravritti, yagyas bring material possessions, life in accordance with natural law (dharma), and heavenly bliss. In time, this brings growth both to the individual and his culture.
As the individual matures spiritually, the desire to perform yagyas takes on a new dimension. The yagyas are performed for the good of creation, without any particular desire other than the well being of all (loka kalyana). This helps to clear away one’s past karmas.
It is said that ultimately, the goal of pravritti is to experience the bliss of the gods, while the goal of nivritti is to transcend desire and to experience the bliss of Brahman. In nivritti, the effect of yagyas is to bring liberation (moksha).>>