Thanks Kapz786! I had already been to their website, but I didn't fully understand... To mine using NiceHash won't you have to use their client? Why does xmr-stak have an option for this?

Moreover, if I'm using X pool (e.g. https://etn.spacepools.org) and say Yes to nicehash, what does that mean? Is it an invalid configuration?

Can somebody please explain me what is "nicehash" when mining with xmr-stak? Thanks!