This technology is similar to cookies in browser and advertisers to know which iPhone user has looked at which ads on which web site. It is anonymous in the sense that no other information beyond your ID is passed to advertisers. It allows different advertisers to do target advertisements, i.e. giving your browsing history, serving you a targeted ad.
Tracking is on by default and the setting to turn it off isn’t in the Privacy settings but buried in the General ones, which is a little ironic.
In comparison, a few weeks ago zdnet reported that the decision of Microsoft to turn off tracking by default and how advertisers reacted, some cranking the crazy talk to unprecedented level (the call to defending democracy had a kitchen sink to it).
It is obvious that tracking technology, supporting target advertising, has become key in the business and we’re certainly not done earing about it!