This is doubly true of you're using complex rigs (e.g. steadicams, cranes, helicopters, etc.) Also, film-outs (the moment a reel runs out) are 100% predictable.

This is doubly true of you're using complex rigs (e.g. steadicams, cranes, helicopters, etc.) Also, film-outs (the moment a reel runs out) are 100% predictable. Crashes are not. That means you're not only having to factor in the time to swap cameras, you're also potentially having to deal with resetting and reshooting the take the camera crashed on. Also, cameras bodies are actually relatively cheap (even film). The really expensive parts are the lenses, which can easily run from 2-10 times the price of the camera itself. And that's before you consider the extra labor required to check each lens out of the rental house, or the cost of insuring them while they're on the job. So unless you also want to double your supply of glass (which triggers a slew of additional charges), constantly swapping bodies means a lens change every time as well. If you're working in an even slightly dusty or moist environment, this is even more undesirable.