Indeed, data outside the application folder usually consists of a preferences plist and saved application state. Of course, there could be caches as well, which

Indeed, data outside the application folder usually consists of a preferences plist and saved application state. Of course, there could be caches as well, which could take up a fair amount of disk space. But I think the primary argumentation in favor of what macOS does now on drag-to-trash is that the users preferences are preserved, for when they install an application again.