My question applies not only to multimeters, but all devices which require a low or a high impedance at the input or output.
Based on my understanding, a device would require a high input impedance, so that the input signal does not get affected by it. In other words, if the circuit was like shown below, then at point A, the effective input signal would be like an output at the voltage divider, hence Rinput / (Rinput + R_source), but since R_input is large, this value will likely become close to unity.
Am I correct in understanding this? Also, is it the same reason multimeters have a high impedance? I.e., so the measurement is not affected and is correct?