I am trying to create a project with minimal size of the project files. I think I should be able to use the “unsafe” method of referring to the audio files, rather than copying them into the project. But I can’t get that to work. I have changed Import/Export setting to “Read uncompressed from original…”, and tried both “Do not copy any audio” and “Ask” in Projects setting. But when I import an MP3 file it seems to read it in, and the xxx_data folder is 42MB for a 2MB MP3 audio file. And it obviously is not accessing the original MP3, as I can move or delete that file and Audacity version still works. What am I doing wrong?? Oh, I’m on Windows 10 and Audacity 2.2.2. Thanks for any help!
Okay, I think I get it. The key is “uncompressed”. Audacity has to work with WAV files, whether saved in the project, or referencing the original files. So I still have to have either the large WAV files (optionally with small project file), or use MP3 files, which will be copied to the project in uncompressed format. Can’t have your cake and eat it too?? 
That option is not available in current versions of Audacity. As you have noticed, the benefits were not so great because Audacity still needs to decode the files before it can edit / process them, and the down side was that if you don’t retain the referenced files in the same location, the project self destructs (Audacity will not be able to find the files).
The current version of Audacity is 3.0.0, and the project format is a single, self contained “.aup3” file. These files tend to be big.
For a small file, export from Audacity to create a normal audio file. “Compressed” formats will give smaller files.
Audacity 3.0.0 supports “Opus” format, which is an audio format that can manage extreme compression with surprisingly good quality.
Example: A 5 minute stereo music track in less than 600 kB:
If your media player does not support Opus, try Foobar2000 or VLC (both are free).
The current version of Audacity is available via the Audacity website: https://www.audacityteam.org/download/windows/