Yes... the latter. Have friends that were census workers in 2000 and 2010. Its a pretty shity job but somebody's gotta do it. So they hire a lot of people who are trained to be really polite and patient and go talk to people. The stories they have about the interactions are both hilarious and frightening.
When they showed up at my door in 2000 I was in the middle of a brake job that was going very badly and I was filthy and in a terrible mood. The very nice lady didn't even bat an eye at it.
Oh - the visit isn't quick. Its a lot of questions. You won't want to stand there in teh doorway with full arms.
.. .this is why its so much better to just do it online now. Or mail the damn thing in.
once you've lived through a couple as an adult... you understand.
And as much as people gripe about it, it's super important. It literally determines your representation in Congress and by proxy, your voting power. There is always a big hubub b/c some states end up losing representatives and others gain some.
The info is also used for local and state elections, determines how electoral maps may need to be redrawn and such. So, sadly, it also gets political very quick.
Most tallies of the population are just based on various guesses and estimates. This is the only one that they literally go door to door and try and make sure that they literally try to count every head. Its a such major effort that takes years and billions of $$.