When visiting a website it puts a cookie on your browser and tracks your movement. To some this seems invasive of their privacy and disallow them however, they are there in order to provide the owners of that website data on how any/all users interact with their website. That data can later on become invaluable in allowing them to develop targeted campaigns to buyer personas.
It can also be beneficial to the user as cookies also store/save passwords to make signing in faster and deliver the targeted promotional campaigns.
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