A lot of scene faders use a full screen black texture with varying alpha to do the fading. During the lifecycle of a game, fading only accounts for a tiny fraction of the time.
So the vast majority of time when it’s not fading, there’s a huge texture on the screen with alpha=0.
Does Unity or indeed the graphics subsystem still evaluate and process transparent textures as if they were opaque?
A definite answer rather than educated speculation please.
Yes they do, and here is a great talk from Unite Europe on optimization. Around the 2330 minute mark he begins to talk about the Unity UI, and shortly thereafter talks in depth on how the UI system works, as well as the question of alpha’d textures. Around 25 minutes he shows a slide and talks specifically on alpha’d out quads and says “if you have alpha’d out quads on the screen you are still paying sampling costs for them, don’t do that.”
The entire talk is fantastic and I would highly suggest giving it a listen!