Explanation of Correct Answer: A benefit of running tests with a test automation tool is that the time spent on repetitive tasks is reduced, as the tool can execute tests faster and more reliably than humans. Therefore, option D is correct. Option A is incorrect, as test coverage is not increased by using a test automation tool, but by designing more effective test cases. Option B is incorrect, as the number of found bugs is not reduced by using a test automation tool, but by improving the quality of the software under test. Option C is incorrect, as the total cost of the test project does not always decrease by using a test automation tool, as there are costs associated with developing and maintaining the automated tests.

References: Certified Tester Foundation Level Syllabus, Section 6.1