Periodically there is a post on the Rhino forum by a user that has seen their relatively simple file grow to a huge size and they don't understand why or how to reduce the size back to “normal”. This article will attempt to explain what has happened and why; as well as offer some possible fixes.
Several things can dramatically add to file size:
Having read the above, you might already have some “usual suspects” in mind. If so, you may be able to skip this section and go to the “possible remedy” section below.
However, if you are stumped, or just want to see all of what your file contains in extreme geeky detail, you can use the Audit3dmFile command inside of Rhino. You can run this on the Rhino file you currently have open or even some other 3dm file on your computer. A text window will open with a lot of info. The top section will be some info about your Rhino installation and what plug-ins are loaded. Below that comes the interesting part - the various “tables” where information is stored in the Rhino file being analyzed.
Some other things that can be tried if all the above fail…