A scene to produce a 2D texture image (for use in another scene) consists of one camera and one rectangle. The rectangle uses only one shader - Emission. The Emission's color and strength are controlled by a fancy nodes setup using images and perlin noise. There are no diffuse, glossy or other shaders. Just Emission. There are no other objects in the scene, nothing to bother rays/paths between the camera and the glowing rectangle.
Do I need to render with multiple samples?
Of course, I did the obvious and set Cycles' Render Sample to 1, and the result looked fine. But maybe I have a quirky scene that happens to do that. There doesn't seem to be any sources of randomness in calculating any one pixel again. Rendering with hundreds of samples is necessary only if there's scattering such as with Diffuse of Glossy. Am I right?