Thicker film stencils require more light exposure. The exposure calculators are offered by the emulsion manufacturers and sold through their distributors. Once the time required to expose film is determined with the exposure calculator, then every time that stencil thickness is selected the screen printer will know how long the light must be on to avoid over or under exposure. Scum and white foam that develops when washing out a screen can be avoided just like the problems of over exposure. Screens can be made satisfactorily the first time thereby avoiding wasting time and materials making screens a second or third time.
People have two complaints about film products.
First they say it is expensive. So cost is not a good argument on small images. Film could appear expensive on large images and short print runs. If small details, edge definition, and surface texture are not a problem, then liquid emulsion might be better to save money. The other complaint people have is they have difficulty applying the film to the mesh.