The upside is that you can know everything of almost any person as well. Whether that upside is beneficial for you is a different matter.

Oh, but of course there is. He you ever seen arguments from the other side? It is to catch criminals of various sorts (money laundering, trafficking, smuggling goods and people, terrorism etc), to keep children safe etc etc.

Also,it can help you uncover and put behind bars your dangerous political enemies. That the tables may turn and the shoe may be on the other foot soon, that's too abstract of a thought to occur to most of them.

It tracks terrorists' efforts to acquire the bomb.