The videos in Istanbulin's link all show useful ideas for bunching, and confirm that you have a lot of latitude in how you go about it.
I started out accordiopleating my flattened filler leaf in making a bunch, since I had been routinely pressing my leaf flat to go into my little kiln. I probably rolled between 500 and 1000 cigars that way. The pleats do allow for better air flow than simply rolling up the flattened leaves within a binder. What I found was that the filler leaf needed to be in a slightly higher case, but it generally worked well. I think the pleating method is particularly well suited for bunches that will subsequently go into a cigar mold, since the final gauge of the bunch is more predictable.
Once I had access to more filler leaf that was kilned as whole, hanging leaf (usually quite curled up), I found that scrunching each leaf strip individually, then combining them and cutting to length prior to hand bunching yielded even better air flow, and can be used with somewhat drier filler leaf. Since I seldom use my cigar mold (occasionally for "gift" cigars), hand bunching is the only method that I use now.
Bob