High impedance inputs are preferred on measuring instruments such as voltmeters or oscilloscopes.
When testing, they are often difficult to probe as the impedance of an oscilloscope or multimeter can heavily affect the signal or voltage on the node.
The signal is neither driven to a logical high nor low level; this third condition leads to the description "tri-stated".
The high-impedance state of a given node in a circuit cannot be verified by a voltage measurement alone.
If the node is not in a high-impedance state, extra current from the resistor will not significantly affect its voltage level.