QUOTE(mwl1 @ Feb 21 2009, 10:04 PM)

I think drawstops are much better.
Agreed! There's something far more satisfying about pulling out a stop inscribed "Contra Bombarde 32" than flicking a switch, I've always felt....
QUOTE
How many people play old organs where the combination pistons are actually useful?

In considering the way in which combination pedals used to be set up, we need to actually see them in the context of organ playing at the time these pedals were in fashion. A Victorian or an Edwardian organist had a desire for varying the tonal colours available to him as much as organists of today have (well, excluding the neo-classicalists...

) - if not more! Whereas we might have, say, six or eight adjustable pistons per manual (and multiple memory levels, generals, sequencers, etc), our predecessors would have though themselves pretty fortunate to have had 3 combination pedals for each of the two main manuals. These combination pedals weren't necessarily set up with stop combinations the organist would have used most frequently
per se, but as a method for allowing the best flexibility with limited resources for stop changing other than by hand-registering alone. This method involved a technique of combining both the use of the combination pedals and the technique of hand registration at the same time.
This is best explained by an example. Imagine a fairly substantial Victorian Great organ. Such a division might typically have a diapason chorus at 16, 8, 8, 4, 2 2/3, 2 foot pitches, and a 3 rank mixture. In addition to this it will have flutes at 8' and 4' (probably Clarabella and Harmonic Flute), perhaps a Dulciana, and an 8' Trumpet. It has 3 combination pedals, most likely set as follows:-
1, Clarabella 8' + Dulciana 8'
2, Small Open Diapason 8', Clarabella 8', Principal 4', Harmonic Flute 4'
3, Double Diapason 16', Large Open Diapason 8', Small Open Diapason 8, Clarabella 8', Principal 4', Harmonic Flute 4', Twelfth, Fifteenth 2', Mixture III.
Number 1 will, on its own, be likely to produce a pleasant sound. However, immediately after depressing the pedal, the organist could push in one of those stops by hand, and produce a different tone. This would allow, say, the reduction from a diapason chorus down to either a Dulciana or to an 8' flute, or from flutes 8 and 4 to one of those single stops.
Number 2 allows for interesting possibilities when coming down from a fairly substantial selection of stops, or for coming up from quieter combinations or single stops. Pushing in 2 stops after pressing the combination pedal allows the organist to either use flutes 8 and 4, or a diapason chorus at 8' and 4', or a warm combination of the two 8' stops combined. Or a diapason at 8' and a flute at 4', or a flute at 8' and a diapason at 4'.... You get my drift! The stops set on number 2 might not be intended to be used as set very frequently, but as a flexible method for getting a selection of different sounds from just one combination pedal.
By making slight adjustments by hand to what is set on number 3, the organist could end up with Full Great (by adding the Trumpet), Great to Fifteenth (by pushing in the Mixture and, perhaps, the Double), or a different weight of diapason chorus (by pushing in the large open). The addition of the flutes is unlikely to make a significant difference in the tone of the full flue chorus, but will certainly help to obtain a smooth diminuendo when pushing in stops by hand which couldn't be achieved nearly so easily if only the diapasons were used.
It can be quite revealing to come across an organ which has the combination pedals still set up as its maker designed (nowadays less likely, alas) and to explore the possibilities. They are certainly more flexible than an organ which has had its combination pedals adapted to suit more modern tastes.