I don't really think there's any benefit to free mining. It takes a lot of processing power to mine anything and see a decent return, as well as raw energy to power everything. These things cost money, why would anyone be giving away money for free? Would you? You have to ask yourself one question, what could possibly be their motivation, if it's truly not a scam of course. I think it's bullshit, personally, but if you're having success with it more power to you.