In cases where you are using distinct, its possible that when a user lands on a product display page (PDP) from a product listing page (PLP) and they then switch to a different variant, for example a different size, the item they will purchase will have a different objectID from the one returned in the search results.
In this scenario, it is best practice to send the objectID of the variant that was returned in the search results and clicked on by the user, ie. the one displayed on the PLP.
This ensures the click and conversion events are associated with the same objectID allowing the product's Analytics to be tracked more accurately.
The queryID sent with the event will also be used to link the events back to the original search. Features such as Dynamic Re-Ranking require that the objectID sent with an event matches the objectID returned by this corresponding search queryID.