The main usage of these sites is for business/law enforcement AFAIK. From my understanding, when you register for an account on some of these sites, there is basically a vetting process to determine what type of entity you are (ie, individual or corporation). Based on that, you are given a certain level of access to info. It has always been my understanding that certain entities, like insurance or law enforcement, get greater access. I've only experienced it from the corporate side, so I can't confirm 100% what the specific differences are. I won't mention which one I've experienced, but it is neither of the 2 listed in the subject line.
You still need a decent amount of base info to locate a person. Unless they have a super unique name and literally the only person in the USA with that name, you'll need more info to narrow down searches. If you have a SSN, then obviously that is the easiest way (although you'd be surprised how many "duplicate" SSNs show up in states that border Mexico lol). These sites also don't always have up to date info....they may report former addresses as current addresses and display alleged former addresses that are actually current addresses. Social worker facilities/churches can even sometimes show up as addresses if the person has been in and out of them.
That being said, in my line of business, a site like this is a HUGE tool. Some people might get wary/paranoid when we find them (how did you find me!?), but it's usually to give them money they are owed rather than be forced to turn it over to the state.