It's not perfect, but if you monitor in mono, there won't be any ugly surprises in the edit room. In the perfect world we live in, everybody does everything right all the time. For the most part, the inputs and outputs on professional audio equipment utilize balanced interconnects. To use a microphone as an example, a positive pressure at the diaphragm will produce a corresponding output voltage on the positive leg of the output. Balanced signals typically interface with three pin XLR cables and connectors.
Standards exist to insure proper polarity for three pin XLRs.
They don't agree. The best place to begin this kind of operation is with your interconnecting cables. The easiest way to do this is with a cable tester, but any continuity tester or volt meter will do. Confirm that each pin on one end of the cable connects to the corresponding pin on the other end of the cable. The best way to start is to check the specs in your owner's manual and see if the manufacturer refers to polarity.