Factory can't assist another factory or unit (army).
Factory can assist another factory.
For example we have factory A and factory B.
Factory A have repeated built query with Medics.
I select factory B, then right click on factory A. Then factory B help factory A to build its query.
Units built in factory B go to rally point of factory A.
Factory can assist unit.
If I select factory and right click on unit - every unit built in factory should follow to specified unit with "Guard" command.
Factory can assist army.
If I select factory and right click on army - every unit built in factory should join specified army.
Goal of this feature - get rid of some annoying micromanagement and allow player to focus on more interesting things.