Find the sum of all elements in a binary tree that fall within the range [low, high], where 'low' and 'high' are integers.

Focus on implementing a depth-first search (DFS) or breadth-first search (BFS) algorithm to traverse the binary tree. As you traverse, check if each node's value falls within the specified range [low, high]. If it does, add it to a cumulative sum. Be prepared to discuss edge cases, such as an empty tree or all nodes falling outside the range, and how your solution handles them. Additionally, consider the time complexity of your approach and how it can be optimized.