In a potential energy measurement experiment, why should an object be lifted slowly at a constant velocity?

In a potential energy measurement experiment, why should an object be lifted slowly at a constant velocity?

When we apply a force to an object and move it in the direction of the force, we say that we have done work to the object.
The minimum force required to lift an object is \(mg\;(≒9.8×m)\). Forces less than \(mg\) accelerate downwards due to gravity, and forces greater than \(mg\) accelerate upwards. When an object is accelerated, a portion of the applied work is converted into kinetic energy as well as potential energy.

The amount of work done to an object can also be represented as a graph. In a force-distance graph, the amount of work done is equal to the area of the graph. (Mathematically, it is called ‘integration.’)
If the magnitude of the force that lifts the object is not constant, the shape of the graph becomes jagged. This makes it difficult to find the amount of work done on an object with ordinary multiplication formulas.