Whenever a potential customer clicks on your ad it might be that he is potentially interested in your product or service but he simply doesn't have the time at that moment to actually make a purchase.
Subsequently, the customer forgets about your product or service. By setting up a Google Remarketing campaign you can remind your potential customer of your website by placing your ad on other websites, which the customer uses.
Let's take a look at the following example: the potential customer searches the web looking to buy 'mini drones'. He sees your ad, clicks on it and checks out your website selling drones. In the end for whatever reason the customer does not make a purchase. The following day while looking at the weather forecast on a different website, your ad, which advertises mini drones, pops up. Clicking your ad on that website guides the potential customer back to your landing page reminding him of your offering. Ideally, the user then actually makes a purchase.
Google Remarketing allows you to maintain a connection with customers who had previously abandoned your website without making a purchase.