Before understanding the importance of defects, let's understand what a defect actually means in the software industry. When teams start working on a part or component of the project, they start building it with a predefined set of requirements or conditions. Similarly, when the test team creates test cases, they base them on the same set of requirements for the respective components.
Now, during the test execution phase, the test team starts validating the actual product in the test environment by interacting with the application step by step, since the end user will perform the same actions, and compare them with the expected results. If the result matches, testers can pass the selected step or test case. However, if the results are different, then we refer to it as a defect.
There are various reasons why the testing team would want to track the issues that occur during the development of the project. Some of the pros and cons are listed here...