If you take portraits with speedlights you may well need to see where that light goes. Remember last night’s portrait? Here is one last version of that:

As you see, I have now finished the picture by adding a background light. Another speedlight, with a snoot (the 5″ Honl snoot). The snoot aims light on to one part of the background only.

To see where that area is, you need to fire the flash.

And one good way to do that is to fire a test flash. See that red button on a Canon speedlight?

That’s right, button. That red light is not just a red light. It is also a test button. Press it and the flash fires, so you can see where the light will go.