Perhaps the best-known use of the "trick" couplers can be seen in the Blackpool style of theatre organ playing.
When Reginald Dixon became organist at the Blackpool Tower Ballroom in 1930 he inherited a small Wurlitzer of 2 manuals and 10 ranks which was inadequate for the space and the purpose. After first proving that the organ could do the job of accompanying ballroom dancing - which he did by way of devising his unique style of rhythmic playing - he was later successful in getting a new organ installed in 1935. This instrument, of 3 manuals and 14 ranks, is considerably more powerful than its predecessor. I understand that "trick" couplers were added after World War II, modelled I believe upon those specified in 1938 by Reginald Foort in the design of his travelling 5/27 Moller organ. Eventually this feature became common on many British cinema organs, to the extent that more than a few instruments were built which included a "coupler" manual - usually the top one - which had no speaking stops but was loaded with couplers. Sometimes the coupler manual would also be used to control certain tuned percussions and - in the case of Compton organs - the electrostatic electronic division known as the "Melotone".
The typical "Blackpool" sound is derived from coupling the Great to the Solo at various pitches including quint and tierce pitches. A good illustration of this can be seen in this YouTube clip of John Bowdler at the Tower Ballroom organ.
https://www.youtube.com/watch?v=YbLD9OXl0lMHere he frequently uses the Solo manual with the trick couplers to add extra punch to the melody. For the most part he's not relying upon the actual speaking stops drawn on the Solo (as they are most likely duplicating what's already there via coupling from the Great) but rather he is using it as a coupler manual.
The Solo stops are at the far right of the horseshoe sweep, and the trick couplers are the cluster of black tabs at the left end of the upper row. The Great stops are across the centre. Notice how he varies the sound of the Solo not by changing the Solo stops but by changing Great stops which are then coupled up to the Solo. The trick couplers are especially pungent when used with the piano. You can see how he often adds the Piano 8 stop by hand to various piston combinations, playing it straight (on the Great) then with the trick couplers (on the Solo).
Andrew