It’s not zero — those -retain and -release calls still exist when necessary and have a small penalty — but it does minimize them well, and is lower overhead and vastly more predictable than GC.
It's a little better than that, because the overhead of ObjC method dispatch is avoided. There are no calls to -retain or -release (if the receiver hasn't overridden those methods), it's just a C function call to objc_release et al. No objc_msgSend involved.
