Floating common

Is there any literature out there or would someone be able to explain this practice to me. We are sourcing an analog signal and the commons on our analog cards are isolated in our enclosure and are all tied into one terminal block and that terminal block is then connected to a ground point near where we tie our signals in.

Just some explanations of how it works and why its done would be great.

the source voltage is +/- 10Vdc

Google "single point ground", "common mode noise", "ground-loop" and "ground impedance"