Difference between airbrush and soft edge paintbrush?

[daeyeth]

I've searched for this but I haven't found a satisfying answer.

What's the difference between toggling airbrush than just using a soft edge paintbrush with opacity or flow pen pressure settings? Like I see some digital paintings and the artist specifically says that they used the airbrush. I'm not a painter so I don't understand what they mean.

[hecartha]

You can see easily the difference doing just that:
-use a round brush (hard or soft, it is not important) with these settings -> opacity 100%, flow 10% with black color
-start a brush stroke on white background without activating the airbrush and stop any movement without releasing pressure and observe
-Now do the same with airbrush activated.

When airbrush is activated, you can hold pressure increasing progressively opacity to the value you set to your brush till you release pressure (100% in my example).
The airbrush setting is good when you prefer to increase opacity progressively holding stylus pressure instead of using many brush strokes which is far less natural for gradient.