Assuming that all code paths are actually exercised in development/testing with strict in effect, I would expect a testing cycle to prove that the program is type-safe with respect to hard-references/other-data, such that symbolic references could not be encountered at runtime that were not seen in testing. This requires that the tests are actually thorough and near-exhaustive.

For our questioner, that is a very large assumption and I would not be surprised to find that the code that produced this question has no testsuite.

In terms of runtime performance, I doubt that strict 'refs' has any effect at all: perl must check for symbolic references in any case as it can never assume that a dereferenced value will actually be a reference and the only difference is whether a possible symbolic reference is considered or an error immediately thrown when dereferencing something other than a hard reference.