When using virtual scrolling and grouping features (currently achieved with kendoGridGroupBinding directive), the ability to control the expanded state of the groups is disabled due to limitation.
The available methods are helpfull when you want to control the state of the groups at runtime, but are not compatible with virtual scrolling since the records are loaded on demand. 
It would be nice if we had the ability to collapse and expand all groups of the Grid programatically when using virtual scrolling.