The goal of any properly designed mixer is to provide all these functions with a minimum of effort by the operator and with no loss of signal fidelity. To better understand console specs, let's figure out what the hard parts are and concentrate there. In general, the most apparent sonic artifact is noise. Even the best designed mixer has noise. To better understand this, let's look at what noise is and where it comes from.
Heat causes electrons to bounce around.
Electrons bouncing around in a resistor generate small, random voltages. This thermally induced current is characterized as a power that varies as a function of temperature. The larger the resistance, the more voltage, even though the power is constant. The voltages are very small, typically measured in nanovolts, or a decimal point with 9 zeros. Thermal noise can generally be ignored when dealing with line-level signals.