From FreeCAD Documentation
- Use relative paths for imported parts
- Uses relative file paths to the part files.
- Use absolute paths for imported parts
- Uses absolute file paths to the part files.
- All files are in this project folder
- All project files have to be in the specified folder. It doesn't matter if they are in subfolders of this folder. Note: No file is allowed to exist several times in the folder (e.g. in different subfolders).
This option is helpful to work on different machines because then one only has to copy the project folder.