Well, depends on what you're doing with 70 mm. The original thread was about 116, which is 6 exposures (or 8, for the last 30 years it was made), unperforated, about three and a half feet of film in the newer length. Cutting the reel to take what's likely to still be five feet shouldn't be a problem for that application.

If you're shooting real 70 mm (perforated, from cassettes that look like a 35 mm cassette on steroids), then 13 feet instead of 15 will require giving up some exposures (what, not quite a dozen in 6x7?), but you're still stuck standing in the dark to develop.