Exactly. Medical records are a great example. If you get a new doctor, you have to give them written authorization so that they can get your old medical records.
They can't just say "look I'm a MD, give me the datas", partly because that would be a felony!
Same sort of regulation, albeit more complicated, applies to NSA.
If they didn't collect so much, it'd be easier to avoid the info they shouldn't be looking at.