ALPHA TEST (discarding fragments because they are too transparent) is cheap and safe. ALPHA BLEND (blending transparent pixels with the background, so that background is partially visible behind the object, like a cross fading) is a more expensive, plus it requires correct exact render ordering.
On the other hand, ALPHA TEST does only cutouts (holes in you objects, or shapes), while ALPHA BLENDS does that plus more things (semitransparent objects). Even simple cutouts look better if you use the expensive ALPHA BLEND (assuming you enforce the right rendering order), than if you use only the cheap ALPHA TEST, because hole borders will look far better antialiased.
If you don't need semi-transparencies (you have only simple cutouts), consider using alpha test only (it is faster, but it will look a little less antialiased).
If you need semi-transparencies, you need alpha blending, but it is usually a good idea to also activate alpha test to make it a bit faster, unless all of the surface is semitransparent with no fully-transparent part.
If you use alpha blending, you also need to use the correct render orderering to make sure that the transparent object is drawn after the back-ground it covers. At that point, you can help performance by disabling Z-test or Z-write (if you know what you are doing).
, so I can't really say if it's internal stuff or if setting it in BRFs might have an use.
