TestLink

When unlinking an executed test from a build, it deletes all its results in every builds. I purposely prevented the deletion of all results.
In consequence, when an executed test is unlinked from a build, the results still exist in the database, and they are still present in the other builds.
When the test is re-linked in a build, its results are displayed again normally, without any loss or alteration of data.

My question is the following: is it still a good idea not to delete test results of an unlinked test case when there is no loss or alteration of data?

On TestLink GUI you never get a feature named 'Add Test Cases to BUILD', but 'Add Test Cases to Test Plan'.
Then there is no way to remove a test case just from a BUILD (it not how TestLink works).
You need to play with TESTER ASSIGNMENT to TEST CASE exec on Testplan+Platform+build, if you want that some test cases will not visible on some build.

Your question is (unfortunately for me) not clear, and also it's not clear what do you need/intend/request/suggest