You are most likely referring to cloud mining, they are all pretty much scams more or less.
You need cheap or free power to make a profit in Bitcoin mining these days.
My question isn't about cloud mining, it is about the effects of applying hashpower to pools.
Why has my question been moved to speculation? I haven't asked any speculative questions.
--Jacob
Leasing access to hashpower is cloud mining. Leasing access to a miner is rig renting.
They are both pretty bad and real owners pass the risk to you with a very low premium.
Mathematically, mining alone yields the same results as mining in a pool over a long period of time.
Pools are just people getting together and sharing the reward if they solve a block.
However, mining a pool reduces variance and since the network difficulty is always rising, it's not a good idea to go for the "long period of time".