A word list is used during penetration testing activities primarily to assist in discovering passwords, hidden directories, or vulnerable parameters by systematically trying various possibilities. They are essential in processes like dictionary attacks, where speed and efficiency can be increased by leveraging commonly used or previously leaked credentials. This differs from a random assortment of characters, which would be more in line with brute force tactics, and custom scripts, which are generally employed for a different set of automated tasks that may or may not involve the systematic input of data derived from word lists. Writing techniques are unrelated and not used in the context of penetration testing word lists.