This was a question I came across recently with a colleague who had a boss that was questioning the use of Google Ads when their website already has a lot of high rankings in Google for their target keywords.
To his boss, it seemed like a big waste of money since he figured most of the people who click on the ads would end up clicking on their organic listings for free anyways, so why bother with the ad?
He brings up a great point right? So what should you do in this situation?
I would continue to run Google Ads but I'd have most of the ad budget targeting our 'branded' terms, meaning if somebody searches for our brand our ad shows up.
Why would you want to do that? Because if your site is getting a lot of organic traffic and is a popular brand, chances are your competition is advertising under your brand term.
Running your own Google Ad for your own branded terms is a way of playing 'defense' so people who set out to do business with you via Google Search are able to easily find you. We don't want them landing on our competitors site and deciding to purchase from them instead.
I'd also find out which search terms we aren't ranking for that we could still target via Google Ads. Just make sure to add any terms you rank well for already as a negative keyword in Google Ads so you don't cannibalize your organic rankings.
If after doing all of this, you notice a dip in sales, then you'll probably want to advertise again on the keywords you rank organically for. Why? Because your competitors are and any chance you can reduce a potential customer clicking over to a competitor is one more sale you're likely to get, even if you do rank organically for the keyword.