There's more to it than cost. A tester will tell you how much in error, whether it's consistent, will allow you to test any shutter at any time without wasting film, and without waiting for processing. You can test a shutter in the field or studio too. It's the difference between working carefully and methodically, or proceeding by guess and by gosh.
Originally Posted by Peltigera
Personally, I can't afford to waste film be it color, B&W, 35mm, 8x10, etc. Goes against my grain.