Many people have probably done this: disconnecting the “ground” of the oscilloscope’s power supply 
as shown in the figure below:
Initially, I didn’t understand why the “ground” should be disconnected!First, let’s state the conclusion: the ground of the oscilloscope definitely has significance; if it didn’t, the manufacturer wouldn’t provide it!
Let’s first look at how the oscilloscope’s ground is connected to the power grid:
When the oscilloscope’s “ground” is not disconnected, if differential probes are not used to measure the 220V AC live and neutral wires, it can be very dangerous. As shown by the red dashed line in the figure below, it can indirectly short-circuit the neutral/live wires to the ground wire. Therefore, many experienced engineers advise disconnecting the “ground”; otherwise, it is easy to damage the equipment during measurement.
If the oscilloscope’s ground wire is disconnected, as shown below:
This method is called “floating ground” and can easily lead to electric shock accidents due to improper operation. When the oscilloscope is in a “floating ground” state, the oscilloscope’s casing and the ground terminal of the probe are at the same potential. When testing AC mains, the casing may carry 220V voltage. If a person comes into contact with the oscilloscope’s casing, current will flow through the body, which is very dangerous.
The parasitic capacitance between a “floating ground” oscilloscope and the earth can directly affect the measured signal, potentially leading to signal distortion and inaccurate measurements.Therefore, during the use of an oscilloscope, it is recommended to keep the oscilloscope’s “ground” connected and use differential probes to measure AC mains.