What is a Half Stop in a Lockback Knife?

Some (older) lockback folding knives have this little addition to their locking mechanism. What is it exactly, and what does it do?
Support the channel on Patreon: / mannixknives

[@ericstarr9399]

Interesting. I have many slip joints with half stops, but I have not seen lockbacks with half stops! Thanks for sharing!

[@Jeremy-Two]

Cool.

[@tvy3-bdx]

The Kizer Slicer and the Kubey Akino both have half stops.