Right. You can only vary chain length in one inch increments, not 1/2" increments. If the ends mate up and you take out the next pin to to shorten the chain 1/2", the ends won't mate anymore and you'll have to take out another pin to get the ends to mate again.

Another way to look at is that a chain has to have an even number of 1/2 links. It's gotta have one inner for every outer. This includes the master link if you're using one.