Chain shortening only one link?
For 1/8" chains as used on singlespeed bikes (or with hub gears), half links are reasonably common.

They do exist for 3/32" chains (which are sometimes used without derailleurs) but are much less common as single speed 3/32" chains are. They're not needed if you've got a test derailleur as the derailleur provides much more chain length adjustment. A chain tensioner can do this on a singlespeed.

The main reason for using these appears to be on singlespeed conversions, when they lack the horizontal dropouts of a frame built for single speed.