In most cases kml to png conversion is used for the purpose of exporting textures from 3D models, in which the texture from a 3D model in Google Earth format is saved as PNG graphics. This is usually done in various 3D modeling tools that support such feature , so pretty much any.
Another way how to look on this conversion would be just to create a raster preview of the 3D model, also doable, also common feature.
Updated: February 6, 2023