The only reason i would use one is to get cheaper steam keys from brasil and for that i can get a free one.
From a security standpoint it is awful because you increase the number of providers you have to trust.
Apart from your ISP and the server you connect to, you got a third party involved for no reason.
And VPNs can not that trustworhty as shown by the leaks of logs and what not.
Maybe someone can enlighten me why these services exist and what usecase they have?