In SketchUp, we always have to balance between performance and quality. We try to keep poly-count, image sizes low, use styles that are faster while modelling etc. This is also the case with image transparency. While modelling, try to use a style that is fast enough but when we want to export our final 2D output, of course, we want to have the nicest images possible. In SketchUp, you can notice that sometimes - when images with transparent areas are "stacked" in front of each other - there is a rather "ugly" halo around the images. This is due to some style setting however and can be overcome when we export images.