It was decided in #283 not to duplicate the functionality of loadValue: [0, 0, 0, 0] with a loadValue: "zero" or similar.

However, in the time since then, I've seen numerous users trip up on this, using loadValue: "load" when it's not necessary, because doing the simpler thing seems like it should be the "better" thing.
Of course, [EDIT: if in the same command buffer or on a late-recording implementation] loadValue: "load" gets replaced with loadValue: [0, 0, 0, 0] if the render target happened to be in an uninitialized state before the render pass, so in many cases it's not actually a pessimization. But I think we should make the "fast" option more accessible.