c) Test quadrants allow stakeholders without technical preparation to more easily understand different types of tests, as well as that some test types at certain levels are more important.

d) Test quadrants enable agile teams to develop a communication strategy based on classifying people according to the four main psychological types and modeling relationships between these individuals.

b) Test quadrants help assess high-level coverage (e.g., requirement coverage) based on low-level coverage (e.g., code coverage).

a) Test quadrants facilitate test planning by dividing the testing process into four stages corresponding to the four basic levels of testing: module, integration, system, and acceptance tests.