Allows resource packs provided by servers to be overridden and moved.
Exactly as the title says, it allows resource packs provided by servers to be overridden and moved in the resource pack menu. That's it.
Up to date version of https://www.curseforge.com/minecraft/mc-mods/server-pack-unlocker which was likely abandoned
To fully disable a server's resource pack (and prevent downloading it) you can change the server resource packs setting to "Disabled" as seen in this image below

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