Lazy loading is an extremely important concept. Default lazy loading is turned on, which means the child object is not loaded (Sql sent to backend), until you actually access the object in code. As you can imagine this is a major performance improvement.
Some more information about Lazy Loading can be found at :
Some explanations on lazy loading
 | For each mapped Relation you can override the default setting for Lazy Loading. Please read Relation Mapping for more information about this topic. |