Ancient Indian texts state that achieving knowledge of Atman (the true Self) is the goal of tapas. It is also sometimes referred to as a spiritual rebirth or transformation.
Yoga practice is linked to tapas in that both require meditation and periods of calm reflection. Indeed, it is said that yoga is a type of tapas, because of the discipline and effort necessary to practice yoga in a meaningful way. The self-contemplation that happens in yoga practice can help lead one to a better understanding of their atman, which is the goal of any tapas.