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GEO files can be big. This is partly because they are text files (readable in let's say Notepad), but also because they often contain repetitive information (for example, even a tiny facets with default parameters takes about 20 lines to write).
There is also a problem related to this: sending them by email or sharing over Dropbox might result in the browser interpreting the content (ie. displaying the GEO file as a webpage instead of downloading, the email client putting the file content in the email, etc.).
Good news is, because of this uncompact and repetitive behaviour, they are very well compressible. It is not common to have 2% compression ratio, converting a 100MB GEO file to a 2MB GEO7Z file.