There are several reasons you, as a developer, should be concerned about the size of your application and be actively trying to reduce APK size as much as possible. For one thing, there are potential users of your application who might be limited by their data plan, connectivity, or storage space on their phones. Offering an application with size of tens or hundreds of megabytes could potentially make them think twice before downloading your app and maybe even go for a different option just to save the bandwidth.