Imagine browsing an online clothing store. Cookies will take note of the products that you have been looking at, regardless of whether a purchase was made. After exiting the site, ads related to the product or the product itself will start appearing even while you are browsing through other sites. Cookies store your preferences and browsing history to tailor-make advertisements.
When browsing a site for the first time, it usually takes some time to load all the images successfully. After repeated visits, it will take a much shorter time for the same images to load. When a website was first visited, a small part of all the images was stored in your device. This makes the loading time for your subsequent visits faster. The only delays would be from new resources/products that are added to the website.