How to deactivate a subform

The task or programm associated with a subform will be executed whenever a subform refresh happens (eg. scrolling through a table)
This is not always desirable. Suppose you have a tab control on the page and in some tab's there are subforms defined. All the subforms will be executed, although most of them are not visible.
When you set the subform to visible=No then the subform will not be executed.
So you can set the subforms on the tab control to be visible only when the associated tab is active.