What does a pre out do?

Thank you Newbee.I appreciate your help!

Thank you Tnkujry!
If you hook up a sub, does it take power awawy from the integrated to the speakers? Or if you isolate the preamp and use another power amp, what happens to the power that the integrated is using? Does it cut off the power?
Thanks for your help!

Thank you Marakanetz. Then would it be okay if you purchased an integrated amp with dual binding posts but the speakers are not bi-wire? Is this detremental or would it be okay. Thanks!