There have been questions before about what utility can be derived from a two-octave keyboard in terms of learning any keyboard idioms. Well, two five-octave MIDI controllers and a volume pedal seem to handle the minimal great and swell needs, but what about the pedals? Surely one octave can't be enough; surely one octave controllers are only common for the price? 16-notes and 2-octave pedalboards also exist. Of course, with a 32-note controller I can do anything and wouldn't have to worry about any limitation, but what if I only care about the practical limit of what I can't play? What do these three tiers, one octave, sixteen note, and two octave, bar me from?
One octave keyboards make smooth voice leading impossible. Sure, you can play any chord, but if you want to go from F to Dm, you can't just move the high C up to a D because you don't have that key. On a pedalboard used only for playing bass notes, this is less of a problem. However, it can still restrict your note choice: when playing a V-I in G, you have to use the low D in the bass. While going up a fourth still sounds satisfying, the resolution of the bass going down a fifth is more powerful.
With 16 notes, voice leading gets a lot easier, but you don't have room to accompany a melody with chords. At the very least, you're severely restricted in the type of melody and chords you can play at the same time.
Finally, with two octaves you have just about enough room to play chords and melody at the same time. You are still somewhat restricted in the chord inversions you can play underneath a melody, and in the range of the melody itself.
The standard church and concert hall organ has a 32 note pedal-board. You'd get away with 30, very little of the repertoire uses the top two, just as very little piano repertoire uses the top few notes of the keyboard. (But watch out for modern composers, who delight in using the far extremes of any instrument's range and techniques.)
The famous Widor Toccata requires C to F, that's 30 notes I think? You need to be able to play THAT if you want any wedding gigs!