By default, /home/$USER and /opt are saved to the backup file (/etc/sysconfig/tcedir/mydata.tgz).
If you have lots of data in those directories (g.e due to dropbox), you could either use kernel boot codes to specify partitions where those files will be found (instead of the file system in RAM; plus removing these dirs from backup) or you could create symlinks from some big directories, pointing to some actual storage media. The latter on is what I use (often needs linux file system to preserve file permissions).