This is primarily intended for cinematic single player experiences. A feature that I'm personally surprised didn't make it in the base game.
How it would function is a script call would be made in the SQF File --- something like this.
player lockFreelook true;
Additionally, a second command would be excellent with this --- disabling player movement, similarly how this feature can be disabled by AI - this would essentially keep users from moving around during these sequences.
This would essentially be the same as the user activating the freelook key, except in this case, the player can not exit freelook by their input, but rather freelook would only be exited by script call when it is re-enabled.
The purpose? --- this would help tremendously with creating cinematic experiences in single player missions, such as cutscenes, etc. etc.
Alternatively, it would be nice to enable "AI remote control" where the player would be able to continue to use freelook, but AI would handle pathfinding and movement, and could be used like they would normally without player control - this would allow you to create movement points for the player character while scripting these cinematic sequences.