How do you determine which results (personalize rank vs open search rank) needs to have more emphasis ?

Pasting the blurb from this link - https://docs.aws.amazon.com/personalize/latest/dg/personalize-opensearch.html

"Continuing with this example, if a user searches for a specific type of car from a specific year (such as a 2008 Toyota Prius), you might want to put more emphasis on the original ranking from OpenSearch."

How do you determine which results (personalize rank vs open search rank) needs to have more emphasis ? I understand it might be business and use case specific, but trying to understand any best practices to follow.