...
Whether to use Test-tag or Features mostly depends on whether you want to include the full_regression tests for the specified feature tag. In the future, full_regression tests will not be excluded. Regardless, pr tests are almost always required to be successfully ran for a PR to be merged.
How Do I Identify Which Tags Will Verify My Changes?
When a change is covered by existing unit tests, there is no need to run additional tests.
When a change is covered by new unit tests, you might need to specify the corresponding Feature Tag.
When a change is not covered by unit tests, you do need to specify the corresponding Feature Tag.
E.g. Middleware applications, high-level flows, 3rd-party libraries
List of Frequency Tags
These tags determine when a test runs. Some tests might be ran at multiple frequencies.
...