Color calibration on a monitor is of only marginal use unless the entire computer is calibrated as a set. This includes: Monitors, video cards, connecting cables, interface type, drivers, operating system, etc. Change any one of those items and the entire calibration is thrown off. Let's say you have the entire set hooked up calibrated via HDMI, then switch out the cable to connect it via Display Port instead. You've just thrown the entire calibration out the window.
Having said that, the only people that really need to worry about calibrated displays are those that routinely work with printed material. And these people also have to take their printing setup into account. It's a big mess. That's why things like Pantone were invented. It let just specify a particular Pantone color, and leave the rest up to the professional printers.