ExecutionVariableSnapshotObserver is created each time on task completion and submit form, even when the command doesn't require variables in return. However, this means that process instance variables are always fetched when a task is completed.

https://github.com/camunda/camunda-bpm-platform/blob/master/engine/src/main/java/org/camunda/bpm/engine/impl/cmd/CompleteTaskCmd.java#L64
https://github.com/camunda/camunda-bpm-platform/blob/master/engine/src/main/java/org/camunda/bpm/engine/impl/cmd/SubmitTaskFormCmd.java#L77