Fast input/output (I/O) operations are crucial in competitive programming when you have to deal with large data sets. Slow I/O operations can easily cause time limit exceeded (TLE) errors, even if your algorithm is efficient. One of the most common techniques is to use buffered I/O. In C++, you can use `scanf` and `printf` instead of `cin` and `cout` for faster input and output. In Python, using `sys.stdin.read` and `sys.stdout.write` is faster than `input()` and `print()`. You can also batch outputs by storing them in a string or array and then printing them all at once. These I/O optimization techniques help improve performance in problems with heavy data processing requirements.