Mintmaster
Veteran
I guess, but even if all RTs had the same blend mode, you can still have individual alpha channel values to disable it on whichever channel you want. Decals are just a few pixels, too, so trying to save performance is rather fruitless (and I think some hardware even skips the framebuffer read when it can if the blend factor is zero or one).I was asking myself the same question. Off the top of my head it could be useful to apply decals (bullet holes, blood splatter, etc.) to the G-Buffer. Maybe you want to completely overwrite the normal but blend the diffuse with the existing value in the G-Buffer or something similar. (In theory you'd probably really want to blend the normal too but you need programmable blending for that).
I guess there are some corner cases where you need to add in one RT and lerp/multiply in another.