I once tried a site clowerty bitcoin for free mining and after 3 months , i got three dollars in it for minimum withdrawal, i got my withdrawal that time but after next three months , the site did not pay me . I was still happy by getting 3$ in the first place.
The art of cryptocurrencies mining is still vague to me, although I have heard about it multiple times and even even engaged in some sites that pop up some years back but I haven't successfully mined any cryptocurrencies.
If you have successfully used one and get something to show for it, I'd be interested to know the site and how it works from your experience.