This is just like cloud computing. Where you just pay for devices that are not on your premises but managed by specialized people. Its an interesting concept and worthy to be invested if the company is legitimate.
Cloud mining has not been profitable for years now so anyone thinking about this should reconsider and do something else, besides as we know there are many cloud mining operations that turn out to be scams, when you consider all of this it is not really worth it to try those sites as the chances you recover your money are very close to zero, it is better to consider other options like becoming a trader or just holding your coins over the long term.
Mining itself is no more profitable unless you have some mining farm that has expensive machines. If you opt to do mining with some third party then apart from sharing reward you have to pay for price of miner and electricity, thats why reward is usually low when mining with third party like OXBTC.