As mentioned, so much of this depends on the organ. You take what you get.
Something interesting: Take a look at the specs of almost any Cavaille-Coll organ, and there are always "octaves graves" couplers on the manuals. That would mean "sub-octave", but you rarely if ever see super-octave. As for the "tirasses" (manual to pedal), they are always unison pitch. All of these were done with small pedals above the pedalboard, so running out of room could have been a factor.
Much of this could have simply been the style at the time, or C-C's way of building organs. Nowadays, especially on larger organs, there are often complete sets between all suitable manuals at all three pitches. Notice that some five-manuals have two whole rows of couplers about the 5th manual.
I have sometimes wondered if a four-manual could benefit from having couplers at all three pitches and all manuals, including Great, to the fourth manual, so it could be used as a coupler manual. They usually tend to be the reverse, to the Great. This would seem to be part of the reason for the famous "Grand Choeur" manual on the St. Sulpice organ. It's the only manual that all the others couple to, but it is also a part of the Grand Orgue division, with the reeds and upper work there and the other flues on the second or "Grand" manual.
Needless to say, organ builders all have their own ideas, so unless one is in the happy process of calling the shots on a new organ, there may not be much choice.