Password length is the first password policy that the administrator should implement to help mitigate the chance of a successful brute-force attack. A brute-force attack is a method of guessing passwords by trying all possible combinations of characters until the correct one is found. The longer the password, the more combinations there are, and the more time and resources it takes to crack it. Therefore, password length is a key factor in password strength and security.
References: CompTIA Server+ SK0-005 Certification Study Guide, Chapter 3, Lesson 3.2, Objective 3.2