On a few monitors it say's a huge warning: "Isolation Transformer" needed, can someone explain to me what it is.. and do I need it just for pulling the monitors out or working on them etc.. ?
Isolation transformers do just that... isolate the power being used by the monitor from the rest of the game. That's what all transformers do, because the current flowing through one side of the transformer is independent of the other side. The isolation transformer typically has matched windings on both sides, so the voltage that goes in one side matches the voltage coming out the other side.
Since your monitor runs a flyback at dangerously high voltage, and the fact that no piece of electronic equipment is immune to failure the isolation transformer reduces the risk of thousands of volts accidentally flowing into the rest of the game should the monitor fail.
(although that might be cool to see)