I haven’t used either command, but based on what I see in the manual, rcd tells rclone to start listening for remote commands whereas rc is used to issue remote commands.
Try it out by going to a folder with some files and typing: rclone rcd .
That should open a tab in your web browser with a list of your files.
There are situations where being able to send commands to rclone remotely would be helpful, but I’m not sure that you need to do that in this case.
Technically true, but FOSS isn’t “free” in the sense that someone is contributing labor to build and maintain the software. Free to use, but not free to make. I personally wouldn’t expect or shame a person for using FOSS without contributing. But if you make a profitable business off a FOSS project, it seems reasonable to expect some form of contribution back to the project - not because it is technically required, but because who better to sponsor a project than someone profiting from it?