Compounds are useful for organizing your ICE trees. Even if you don’t intend to reuse or distribute your compounds, using compounds can help make your ICE trees readable and understandable. Kinda like paragaraphs in written text. Use compounds to separate blocks of functionality, and give your compounds meaningful names. It’ll help later when you come back to an ICE tree you haven’t worked on for awhile.
Consider this basic emission. Looks pretty simple, right? You can tell at a glance what’s happening, and what scene references are used in this ICE tree.
If you explode all the compounds in a Basic Emission, you get something a lot more complicated looking:
Without any compounding, you’re looking at a 195 total nodes (and 46 different nodes).
eX-SI 
The same principle obviously applies to RT Compounds as well
to prevent the Render Tree from becoming too cluttered… 😉