You should choose a test technique because you need to match the way you test to the content of the product under test. A test technique is a method or process for deriving and selecting test cases based on some criteria or rules. Different test techniques are suitable for different types of software products, depending on their characteristics, functionalities, requirements, specifications, risks, etc. Choosing a test technique helps to ensure that the test cases are relevant, effective, and efficient for the product under test. The other options are not correct reasons to choose a test technique. Time constraints are not a factor for choosing a test technique, but rather for prioritizing or optimizing testing activities. Covering the full scope of the product’s functionality is not a guarantee of choosing a test technique, but rather a goal of testing. Choosing a test technique is not a common practice in software testing, but rather a professional skill and responsibility. Verified References: A Study Guide to the ISTQB® Foundation Level 2018 Syllabus - Springer, page 31.