Lazy loading of data means that data loading e.g retrieval from database before the human service launch is deferred for visible and non-visible sections of the coach. The visible section also benefits since the ui is rendered first and then the data appears after 1-2 seconds via ajax calls making a visually faster appearance, you can put an overlay while the data is loading. The non-visible section e.g. hidden tabs also benefit once they are clicked the data loads via ajax calls, you can have multiple input multiple output custom ajax calls and then bind all your data, lists, complex variables to the respective binding and options objects.
Lazy loading of rendering is to disable the rendering of non-visible sections at initial load and on activation of the tab hidden section render it, this comes as a feature of Brazos enterprise toolkit and was recently introduced, you can also create a custom section implementation with lazy loading of rendering, this is esspecially useful if you have huge tabs with a large number of controls/coach views.