hah. I made a similar thread about a year ago, wondering why the professional photographer WASN'T bouncing the flash.
flashpoint99 wrote in post #15956516
Wouldnt a proper defuser have created the same effect without blinding the guests behind her?
In a word, no.
If there's a large light-colored wall behind the photographer, then by pointing the flash directly backwards, she can light up the whole wall - for the purposes of the photo, effectively turning it into a giant light source. Similar concept to a huge reflective umbrella.
The little plastic flash diffusers don't intrinsically make the flash head bigger or "softer." Instead, they attempt to redirect the flash's light in every direction, hoping there's another surface somewhere to bounce off of, to give the appearance of a softer light. In a best-case scenario, the diffuser causes the light to bounce off the ceiling and the walls and onto the subject. In a worst-case scenario (e.g. outdoors) they just waste light and batteries.
In a lucky break, the little plastic diffuser can create a soft light, but it's nowhere near as directional or controlled as pointing the flash at a white wall. Both techniques certainly have their place. But if you're just sticking the little bit of plastic on your flash head, not paying attention to what the diffuser is actually doing to the light, and hoping for some magic to happen ... well, you're rarely going to achieve your desired results.