Panel cleaner is used on a vehicle to clean and restore the appearance of various panels and surfaces. Some of the reasons why you would use panel cleaner include:

To remove contaminants: Panel cleaner can help to remove contaminants such as road grime, tree sap, and bug residue from the surface of the vehicle, making it easier to clean and maintain.
To restore appearance: Over time, various contaminants can cause the panels and surfaces of a vehicle to become dull and faded, and panel cleaner can help to restore the original shine and color.
To prepare for other treatments: Panel cleaner is often used as a preliminary step before applying other treatments such as wax, sealant, or paint protection, as it ensures that the surface is free from contaminants and, therefore, ready for the next step.
To improve performance: Some panel cleaners contain active ingredients that can improve the performance of other treatments and make them last longer.

Overall, panel cleaner is a versatile and effective product for anyone looking to restore the appearance and performance of their vehicle.