Any test that doesn't bring value is a waste and should be deleted, because it still comes with the cost of maintenance. The hard part is to discover which tests are valueless and which are invaluable.

As a software tester, it is easy to draw the conclusion that every test provides regression, where regression means that it validates no new bugs appear in the functionality we covered with tests. This might be true in some cases, but it is wrong to make this assumption when it wasn't the purpose of the test. Unit and integration testing may provide some regression testing, but this comes as a side effect and not as its primary focus. In unit testing, the purpose is design, and in integration testing, the purpose is to validate how parts of the system fit together. These purposes have very little to do with regression.

When it comes to functional testing, regression is another matter. In a functional test, I claim to expect some functionality of the system from a black box...