Why are there 2 different coolant temperature sensors? 1989 Ford Mustang 302 Engine

What's the purpose of having an engine coolant temperature sensor for the ECU and a separate sensor for the dashboard temperature gauge? This is confusing me because the ECU temperature sensor is showing temps 20-30*F higher than what my dash gauge shows. So the dashboard gauge sensor is in the lower intake manifold where cooled coolant from the radiator enters and the ECU temp sensor is where it exits the engine right before the thermostat. In the summer time on a hot day my gauge will show around 190-195 and the Tuner Studio software for my Megasquirt shows 210 even up to 230 from the ECU temp sensor by the thermostat. Am I overheating or is this ok? I am able to relocate the gauge temperature sensor next to the engine ECU coolant temp sensor so the gauge reads the same as the ECU but I figure there is probably a reason why its set up the way that it is. I'm just confused because it seems like it doesn't really matter what the coolant coming out of the radiator is because don't you want to know the actual engine temperature the way the ECU sees it?

While it's common nowadays to have the ECU supply the temperature reading to the meters, in the early days that was a complication and it was simpler to use the old style analogue gauges in parallel. It also made engine swaps a lot simpler.

Those sensors usually use different strategies of data displaying. Whilst one sensor is used by ECU for precise temperature measurement which is important for choosing proper afr value in particular condition the other sensor is used by instrument cluster just to display a ballpark of temperature in order not to make a driver to worry about it every time the temperature raises 20-30 degrees- it will stay in OK range unless the temperature goes really high and that's the real situation when you need to do something about it.