Configuration files like YAML enhance flexibility and reusability in machine learning projects. YAML, a popular configuration file type, uses key-value pairs and indentation for data representation. It supports various data types, including numbers, strings, booleans, and arrays. By creating a YAML file, developers can store key parameters and settings instead of modifying source code directly. This allows for easy experimentation and simplifies project management. The PyYAML package in Python can be used to load and access YAML files, enabling the separation of configuration from code and enhancing project flexibility.