You decide what is stored beyond what the shop needs to work. Each category can be switched on or off, and the choice can be changed at any time.
Keeping you signed in, remembering the basket, carrying an order through the checkout and remembering this very choice. The shop cannot work without them, so they are stored without asking.
Remembering settings you chose — the language, the currency — so that you do not have to choose again.
Counting visits and following the route through the site, so we can see which pages work and which do not.
Showing our advertising to people who have already visited the site, and measuring whether an advertisement led to a purchase.