As of this community, it's all about "Earn Money" so I will try myself to explain or give some details about several kinds of free earning sites or applications that we know.
This is only my side.
As far as I know, all free earning sites and applications have a ReCaptcha or Human Verification. It is very important for every people that we must answer the Human Verification so that the developer of the site wIll know people are real, not fake, or using some application.
This is the second thing I consider how they (free earning site or applications) can gain money, is from their "Advertisements". Most of the free earning sites and applications are all about promotions of their different works. "Referring" is also the way how to ease the earning of money.
The high amount of score or points that you can payout. The first thing that we consider in every site or application is "What is the minimum payout?" For me, this is accurate because that's what I considered.
Again, this is only my idea. Every people has their own way to ease the earnings of money. We all have patience and contentment.
As for me, when I search for an earning site, i fo straight to the reviews and user feedback. If they're moatly good then I'll give it a try