Appicon Question

Hello,
I'm new to all this and I am currently trying to portabalize an app that I have installed. I have it working and need to do more testing. I am using the 3.5.0 template. I see additional .png files along with the appicon.ico included with the template, but I only have the icon that came with the app. What is the purpose off the additional .png files and are they needed or recommended?

Thanks...