You don't need to use Alpha blend mode if your clips have alpha.
You can use most other blends also with alpha clips.
Add has a different fade curve, and also a different behavior than Alpha.
With Add at 50% opacity, the pixel color values will be added to the texture below, so for example 50% grey layer with 50% grey layers below will make the output 100% white.
Then with layer at 100%, the output would look like if it had Alpha blend set at 100%
With alpha blend the layer will be faded in over the layers below gradually.
Transparent backgrounds would behave the same in both cases, so you'd see the layers below through the transparent areas of your layer texture.