home.attbi.com/~sbernardi/elec/og2/partsub_pots.html, From the page:
Potentiometers and trimpots can really run up an expense in DIY synth building because you will use so many of them. So when it becomes possible to obtain a number of them cheap, it is a good idea. But then you run into the problem that you have 20 of these pots or trimpots you got for a great deal, but a schematic calls for a different value. When can substitutions be made?