Catalog contains catalog (that you can see on the 'data view' tab). Without it you can use 'archive view' instead. It will be regenerated on the next backup or manually by 'catalog now' function.
Without xml files archives are restorable, too, however xml files will be regenerated automatically during restore and will not contain some information from the original files. For example, if archive contains several full backups, new xml file will be generated for each chain of full and dependent backups. Archive name will be changed to something like Archive_2013_01_20_ ... (i.e. orignal name + date) If you need to continue backing up to the archive, xml files must not be deleted.