[Jens M Andreasen]
A "synthesist" (that's my scenario), who
can't hear *anything* before
the end of the pipe, would be very sensitive to jitter (the deviation,
or "sloppyness", between triggers and actual sound) and would therefore
require the smallest of small buffers.
Trading jitter for constant latency can work well for some, too.
Unfortunately the increasingly popular MIDI over USB connections
already introduce a millisecond of jitter, so if you're already
working at a blocksize of 64 at 44.1 or faster it's not worth the
effort.
Cheers, Tim