Advertisers benefit by placing their ads for free, publishers get the money they deserve.
I think it's a pretty balanced feature. Every ad network should have that.
This is just my opinion though, no need to agree with it
Well I joined Mellow simply because of the free faucet they give. We all love free stuff and hence I am here
Also I got several referrals via mellow ads by advertising my referral links there using simply the faucet credit. To be honest, its pretty much worth it.