How does the 'Zoom' on my flash work?

I dont understand how (or why?) a flash can have zoom. Is there like a little 'snoot' inside the flash head that focuses a beam further? I thought all a flash could do was vary the power output e.g. full strength, 1/8th, 1/16th, etc? Are the two one and the same? I have a 580EXII and thinking of getting a second non Canon flash without a zoom head and wondering if i'm gonna miss this 'feature'.
Any help appreciated!

The zoom function narrows or widens the beam of light depending on the FOV coverage required by the focal length, so as to not "waste" light in areas that fall outside the FOV of the focal length

I always bounce my flash so its never been a "feature" for me, but some may find it useful

Since you have a 580EXII, why not take a look and see what happens when you change the zoom? Hint: Hold in your hands, turn on the power, stare at the clear lens where the light comes out and change the zoom. You should be able to see exactly what is happening and come back and let us know how does the 'Zoom' on your flash work.

you're just saving more battery and wasting less light if it auto zooms for you. Also let's you control how big the appeared size of the light will be depending on how wide it is bouncing off of a surface.

1) For direct flash, the zoom feature dramatically increases the range of the flash over what it could be if stuck at the 24mm coverage setting.
2) For bounced flash, the zoom feature is still useful. I often use it when shooting into umbrellas to keep the light from spilling over the edges. You can also adjust the ultimate size of the bright spot on a ceiling or wall when bouncing off of them which can make subtle differences in the appearance of the light.

40Dude6aedyk wrote in post #7424097
Since you have a 580EXII, why not take a look and see what happens when you change the zoom? Hint: Hold in your hands, turn on the power, stare at the clear lens where the light comes out and change the zoom. You should be able to see exactly what is happening and come back and let us know how does the 'Zoom' on your flash work.

Just make sure you press the right button, i.e. the Zoom button and not the Pilot/Test button.