Easy....
A bike drive train uses a 1/2" link pitch (the distance between each link pin and corresponding sprocket teeth), whether it's a regular or a half link chain. A regular chain alternates inner and outer links, so there are two links (1") required to make joinable ends. There fore your chain is always an even number of links.
A half link combines inner and outer mating ends within one pitch length instead of two, thereby allowing the chain length to be determined by the 1/2" instead of the 1".
The OP's predicament is that at x chain length (with conventionally matching ends), the chain is too slack. Removing two pitch lengths to get z length results in not enough chain. So if we take off one pitch length, resulting in y length , we have the problem of having two ends the same, and they won't join. so we replace one of those end links with a half link, there's the solution.
You can not use half links, either singly or a complete chain, on N/W rings.
