There are times when an organist does "tricks" to make a better sound.
If the building or worship space has little or no reverberation or "bounce," for example, an acoustical release on a final big chord can be used to give the illusion of more reverberation.
This is a device which was given great attention by the late American born organist Virgil Fox (photo) and his acolytes to give the impression of size and space, making the sound of a final chord "bloom" into more of a diminuendo, and seemed to work most beautifully for him when the hands were spread over at least 8 notes covering 2 octaves.
If we're improvising then, in 4 part harmony, and we want to do this type of acoustical release at the end, more voices can be added until we arrive at the finish with at least 8 notes at the point of release of the final chord.
If we're performing repertoire, it works just as well when we use whatever final chords for both hands the composer wrote on the page; some organists take liberties here and duplicate notes in the harmony that weren't written into the score, the object being, of course, to produce a larger, more grand effect [See blog, Poetic License].
The notes of this final chord are released very quickly (but not lightning fast) one by one from the top down, like a bunch of airplanes flying in formation and they all "peel off" together with the lowest pedal note being the last key released.
This maneuver can be facilitated using a quick rotational movement of both wrists counter-clockwise, first the right, then the left.
This wrist rotation can be practiced separately at first, one hand at a time, until the ear hears each note released in gradual and correct order in rapid succession.
Afterwards the hands can be practiced together, working slowly at first to get a smooth "splice" of the hands with no noticeable overlap between the notes taken by the thumbs, then speeding up.
There's another way to do an acoustical release of a big, final chord in spread harmony for both hands, and that's by turning each hand out so that the top note and bottom note of each hand are the only ones remaining depressed until the very end, so that the middle notes of each hand drop out faster and leave the impression that the sound lasts a little longer.
This type of release of final chords in dry acoustics is taught and practiced by certain European organists.
Whichever type of acoustical release is used when performing before a large audience there's no need to throw both hands into the air when that final, loud chord is released, as if the hands were somehow stuck to the keys with super glue up until then; this kind of stage bravura may impress the visual senses of people who don't know any better, but it has nothing to do with tone production and what arrives at the ear of the listener.