One of very common cases is when user modifies java code in editor and saves it. Java and CDI dependencies between classes make it generally a hard problem to do incremental rebuild, but if imports and super types are not changed, we do not need to reset all references to Java model objects in all CDI model objects, as it is done now 'to be on the safe side'. Request to JDT are time consuming and we can gain a lot if only changed CDI model objects reset references.
It is not safe to try this optimization when imports or super types are changed, but they happen not so often as many minor changes.