Disadvantages - can be bulky, give narrow beam, don t take abuse. Disadvantages - expensives and hard to find, require hard to find shooters. Disadvantages - don t work with slaves, have to make your own shooter. Film Author recommends using Kodachrome 64. There is a specific guide number for each film speed with any particular bulb or strobe.
Guide numbers are larger for faster films.
The distance to the camera is irrelevant. This is rounded to the nearest F- stop which is 5.6. This can be done in your favorite cave. Once Guide Number has been established for one film speed, it can be calculated for others. In a small cave that is exceptionally white, under expose by 1 stop.