Necessary
Keeps you signed in, remembers your basket and protects forms from abuse. Always on; carries no advertising purpose.
Functional
Remembers choices — recently viewed products, your delivery area — so you do not set them again.
Statistics
Aggregate counts of which pages are used and where people give up. Never used to identify you.
Marketing
Measures whether a campaign led anywhere. Off unless you turn it on, and turning it off later stops it immediately.