The Use Camera Path option will do the following:
Instead of shooting LC & IM rays from the current camera position (for sampling), V-Ray will shoot the rays from multiple camera positions along the camera path at once.
It will do it for every frame which sometimes helps in samples positioning and in general reduces flickering.
Changing the sampling logic in this way can certainly affect the render time but the difference will vary depending on the specific scene.
Keep in mind that the Use Camera Path options can be used for saving GI light map for the whole camera path by rendering a single frame.
You can then load the map and render the entire animation without the per-frame GI pre-calculations.
This will also avoid any flickering - the GI result will be perfectly stable throughout.
Here’s a short video that demonstrates how this is done:
Note: The workflow is not that reliably in lengthy animations where the camera covers long distances. Some artifacts might occur.