Quote - For example, when I tried out a procedural iris shader by bagginsbill, I had to move the UV center of the iris from (0.5, 0.5) to (0.5, 1.5), because that's where it is in my map.

for me that doesn't seem like a very special case, but if you don't have to do the same thing for a regular image, then only people like me who like to play with the material room are affected.