I don’t want to to take anything away from your discovery, but Bryce has been around for a few years now, and the nature of Bryce users is to explore new ways of doing things differently.
This is a good tip worth remembering for a couple of reasons. The first is animation.
Animating models with bump materials on them (or moving a model through a World Space mode material) can cause a distracting pixellating effect I call shimmer. It’s like the model is being attacked by ants. I made a KEY-FLAME tutorial about it which you can link to in my signature below (KEY-FLAME: Introducing Shimmer). However, if a picture texture is used, even with picture-driven bump, shimmer disappears. Again, see the tute for an explanation.
The second reason addresses terrains. By building a model on a plane, you should be able to convert it all into a terrain by taking an overhead render in Altitude Render mode, then bringing the resulting image back into the terrain editor as an elevation map. Sadly, there are limitations on this technique, were explored by David Brinnen and myself in the last forum, but in a pinch, it might be useful. You can see several examples of this suggested technique in the Bryce 7 Create > Terrain library.
The drawbacks of using this technique for either reason is that it works best for flat plane textures, and not very well at all for curved surfaces. So if you’re wrapping your texture to a sphere, cylinder or complex metaball shape, expect to find a lot of warping and distortion.
In general, images textures are normally drawn using a 2D app like Photoshop or the GIMP, and mapped using a process called UV mapping (in Bryce, UV maps are wrapped to models using the Parametric method).