For example, if I search for "how to do a Subaru oil change" it's the perfect opportunity for the search engine to show me ads related to motor oil, Subarus, car maintenance videos, etc... If I opt in to sharing my location with the search engine they could also show me ads from local repair shops and car dealers.
Later on when I'm reading an article about dog training, I don't want to see ads about fixing my car, show me ads related to dogs. Use the context of the page for targeting.