The 1 1/3' stop (Larigot, etc.), since it sounds an octave higher than the 2 2/3' stop, adds a certain brightness to the ensemble. Its brightening effect is much gentler than adding a mixture. For this reason it can be used as a substitute for or as an intermediate step towards a chorus mixture.
The 1 3/5' stop (Tierce, Terz, etc.) adds the third-sounding pitch. The third gives a rich, reedy quality to the ensemble that reduces clarity rather dramatically.
Some organists add this third-sounding stop in chorus-type combinations, citing historical sources on organ registration. Apart from historical considerations, if clarity is a high priority, it should not be used in chorus registrations.