This is not a garbage collected environment
I have a class instance variable which at some point in my runtime, I need to re-initialize with a different data set than it
If you do myArr=nil; by itself, then you've lost the pointer to which you can send the release message to. There is no magic to release your object.
myArr=nil;
release
And, as Georg says, without being able to release your object, that memory has 'leaked'.