What is pruning in backtracking and why is it important?

Pruning eliminates branches of the decision tree that cannot lead to valid solutions, avoiding unnecessary recursive calls. Without pruning, backtracking degenerates into brute-force enumeration. Examples include stopping exploration when the current sum exceeds the target in combination sum, skipping duplicate elements in permutation generation, and checking row, column, and diagonal conflicts before placing a queen in the N-queens problem. Good pruning can reduce exponential time dramatically. ---