You don't need to know much about microfilms in order to use them wisely, but to many people still, a film is a film is a film – and the cheapest one often wins by virtue of its cost. I have used an analogy many times–but not enough times, I guess. To repeat myself yet again, everyone knows what a fabric is, but everyone also knows that fabrics appear in many manifestations. We have cotton, or silk, or linen, or wool, for example. We also have a host of manmade fibres from which to choose. We can make sails out of cotton canvas and evening gowns out of silk taffeta. We can use whatever fibre and fabric made from that fibre (or combination of fibres – cotton and lycra, for example) we choose, but we also know that each fabric has its own characteristics and its use will be dictated by those characteristics.