Belonging
It's not about what belongs to whom. It's about putting together information (from whatever sources) to draw conclusions on matters proscribed by Data Protection laws.
Even if you visit most sites anonymously, it's very useful to Google if they see the same IP address (dynamic or not) a few seconds or minutes apart.on two or more different sites. It allows them to draw likely conclusions which will soon connect your buying habits, your e-mail address, your taste in pornography etc.
Of course, you'd hear arguments like "Well, we didn't know for absolute certain sure, your honour. it could have been someone re-using the same IP address 30s later" or "It could have been a proxy", But the information needn't be 100% accurate to gain enormous advantage from it (and to cause a great deal of trouble).
A couple of weeks ago, I searched idly for information on laser toner prices, because I knew i'd need a new cartridge in the next couple of months. My next visit to YouTube (not linked explicitly to a Google account) was accompanied by adverts for laser toner. Even at its most innocent, it's like being dogged at every turn by pestering salespeople. Go, Germany!