what is a disadvantage of using diffential staining (dyes to increase the speciman's contrast) in light microscopes?

Staining is essential to observing microorganisms with a light microscope so really the disadvantages of differential staining are those that arise when compared to simple staining techniques or to other microscope types. I's say one disadvantage lies in the fact that differential staining is more complicated and not as easy as simple staining. Another disadvantage could be the fact that differential stains tend to be specific to certain microorganisms, like gram positive or gram negative bacteria, so you can only stain certain species with a particular stain, whereas simple staining allows you to view more variety.