With unperforated 35mm bulk film used in 126 cartidges or 828 rolls you get more! No need for leaders or trailers with the paper backing.
With my old manual 35mm cameras I can load in the dark and shoot at S, 00, 0... 37, 38, 39, 40 if I want but my auto cameras waste a huge leader and refuse to shoot past 36... worse, once in a while they'll decide that a bulk cassette with no DX markings is a 24 roll instead of 36 and rewind early
Once you include the sprocket holes and edges, 135 is a really wasteful format. Convenient, great AF, high speed drive, etc. but very wasteful by film area.