# Why trim then clip in \includegraphics?

Why do we have to follow the trim option with clip in \includegraphics? Is there a situation were trim is used without clip or vice-versa?

The original idea was that trim was just a way of adjusting the bounding box by specifying offsets from the edges rather than a new bounding box with bb, so like the bb key it adjusts the size latex leaves but if the image is really bigger than that it would over/under print the surroundings. clip clips. It's a long time ago and i can't remember all the discussions but probably the fact that clipping isn't the default is related to the fact that not all the important dvi drivers at the time could clip at all.
\documentclass[10pt]{article}