Type of lighting and exposure index. Some films are especially designed for low levels of light or for sensitivity at particular bands of the spectrum. All films are balanced for particular kinds of lighting. Type of filtration needed. Type of processing and printing facilities available.
Few labs process all types of film.
This situation can be especially time-consuming if the film requires editing and must be shuttled back and forth several times. You can avoid much anxiety by getting to know the personnel at the laboratories that process your films and explaining your special needs to them. It may be worthwhile to select films that can be processed by a laboratory directly familiar with your needs.