I'm winding some film using a daylight bulk winder.
I can't see the point of cutting a leader on the film. My cameras seem to load the film fine without a leader. No leader also gives more film for a film picker to grip, so it is easier to pull out the leader after automated rewind.
So what is the purpose of a leader? Were there some cameras which needed them?
Indeed, some cameras do need the leader. Usually they are manually loaded and winded - they use take-up spools with a slot for the leader. Advancing the film is performed by turning the take-up spool, and sprockets alone would not provide grip secure enough. For example, Bronica 135N/135W, Nikkormat EL-W.
When the film has been fully rewound into cassette, retrieving its full-width end would be tricky as you'd have to perfectly align the end inside the cassette to the opening; retrieval of a narrow leader makes this awkward task much easier.
The leader (albeit in a much longer form than on most currently produced films) is also useful for correctly loading film into a bottom-loaded camera (such as LTM Leica, FED, Zenit-1 etc) so you wouldn't have to align the film cassette, take-up spool and bare film all at the same time, which would be quite clumsy and prone to fail.
I think the trick is less wasted film. If you think about the design of most leaders, the leader from one cut of film is also the leader for the next. Since in many (most?) cases, the leader is going to be exposed to light, it is going to be wasted film anyway. By reducing the amount of waste, costs of making the same number of useable frames is reduced.
From memory, the takeup spool in my Nikon FM had a notch that didn't go the width of the film, so yes you had to have the leader cut to be able to insert it.
As long as you have the film lined up properly, it would seem easier to insert a smaller width of leader into a spool than get the whole width in anyway.
The reverse is true when developing. I always cut off the leader - otherwise it tended to cause the film to start unwinding from the developer tank spool.
Here's an image of the take-up spool from the Canon SII manual (Canon rangefinder c. 1940's) The spool has a metal clip to securely hold the film leader to the reel.
This configuration is then loaded from the bottom of the camera, like so:
The clip, not pictured, is a piece of V-shaped metal that holds onto the leader by wedging the leader up into it. It's a decently secure connection that would be more difficult to make if the V had to travel the entire length of the reel.
Not having this connection makes loading the camera impossible or wasteful (requiring you to spool a few frames around the reel to get it to "stick")
Simply, the leader is a holdover from early 35mm rangefinder designs. For those of us that still shoot these cameras, I'm grateful the market hasn't gotten rid of the leader.
