The benefit of alpha-beta pruning lies in the fact that branches of the search tree can be eliminated.
The search time can in this way belimited to the 'more promising' subtree, and a deeper search can be performed in the same time.
Like its predecessor, it belongs to the branch and bound class of algorithms.
The optimization reduces the effective depth to slightly more than half that of simple minimax if the nodes are evaluated in an optimal or near optimal order (best choice for side on move ordered first at each node).