Why is something given away at Faucets?

The idea behind it is to open up the market for new interested parties. If something is given away, people are more likely to take a look.

The site operators finance themselves through advertising banners. These bring in a decent income for the operators and they pass on a fraction of it to you through the regular claims of the Satoshis.

What do the faucets bring me?

For one thing, such "water drops" are great for learning how to deal with cryptocurrencies. This is a great thing, especially for beginners. You learn how to receive and send cryptocurrency. And you can earn a little extra on the side. The important thing with these sites is regularity. 

Is there a catch with the Faucets?

There is no catch. The principle of such "water drops" is quite simple. Attract users to the site and earn money with advertising revenue. You, in turn, are rewarded with these advertising revenues via the claims. 

How many faucets should I use?

The more providers you go through, the higher your earnings will be, of course. Regular visits in particular are usually rewarded with very good bonuses.