None.
When used with the -g or -qlinedebug option, this option records the full, or absolute, path names of source and include files in object files compiled with debugging information, so that debugging tools can correctly locate the source files.
By default, the compiler records the relative path names of the original source file in each .o file. It may also record relative path names for include files.
If you need to move an executable file into a different directory before debugging it or have multiple versions of the source files and want to ensure that the debugger uses the original source files, use the -qfullpath option in combination with the -g or -qlinedebug option so that source-level debuggers can locate the correct source files.
Although -qfullpath works without the -g or -qlinedebug option, you cannot do source-level debugging unless you also specify the -g or -qlinedebug option.
$ xlf95 -g -qfullpath file1.f file2.f file3.f -o debug_version
…
$ mv debug_version $HOME/test_bucket
$ cd $HOME/test_bucket
$ dbx debug_version