The gold standard of software testing is formal verification, a mathematical proof that a body of code cannot fail with unspecified behavior. However, in practice formal verification proceeds at a slower pace than many teams prefer to operate. Fortunately, we have a productive compromise: Fuzzing.
Fuzzing significantly raises the quality bar of software components, closing subtle testing gaps that other approaches neglect to address. For example, validation, a handful of manual tests, and code coverage will still leave latent bugs in very many codebases. This is because the input/state space is many orders of magnitude larger than the number of lines of code, and scale exponentially with the bit width and number of variables.
Fuzzing is able to identify these kinds of bugs, by generating random test cases to more comprehensively evaluate the input and/or state space. Code coverage won't tell you when you have a division by zero bug, or a nil pointer bug, or an empty array