What are the disadvantages of using a diffuser on a flash?

Question

I am thinking of using a diffuser on my canon speedlight flash to soften harsh shadows when shooting indoors. I was wondering what the disadvantages of this might be.

Answer

It will reduce the total amount of light that your flash can put out. It will also use more power for the same amount of light hitting your subject.

When indoors, if your flash can bounce/swivel but the wall is further away, you will probably be better off bouncing without a diffuser.

Harsh shadows are due to a small apparent light source (light travels in a line, soft shadows are when the transition from light to dark is gradual and the object can see part of the light source).

Adding a diffuser barely (e.g. stofen) or doesn't at all add to the size of the light source. The exception is that when walls and ceilings are close, the light is diffused and sent to those surfaces which can create a bit of a larger light source.

Note that when you bounce a flash, it can give a color cast based on the color of the surface.

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