Do you REALLY care if someone knows how to make the PHP interpreter segfault? How to create garbage collection cycles in the JS interpretter? etc. What does kn

Do you REALLY care if someone knows how to make the PHP interpreter segfault? How to create garbage collection cycles in the JS interpretter? etc. What does knowing a language inside and out really gain? "Oh yeah, Java totally does covariance in generics by default, but not contravariance" Is this really useful knowledge?