game trees are important in artificial intelligence because one way to pick the best move in a game is to search the game tree using any of numerous tree search algorithms, combined with minimax-like rules to prune the tree. the game tree for tic-tac-toe is easily searchable, but the complete game trees for larger games like chess are much too large to search. instead, a chess-playing program searches a partial game tree: typically as many plies from the current position as it can search in the time available. except for the case of "pathological" game trees (which seem to be quite rare in practice), increasing the search depth (i.e., the number of plies searched) generally improves the chance of picking the best move.