You create Smart Components from components that you use frequently that require the addition of associated components and features. Examples:
A connector with mounting screws, nuts, screw holes, and a cutout
A retaining ring with a groove
A motor with bolts and mounting holes
When you make a component smart, you associate the other components and features with the Smart Component. When you insert the Smart Component into an assembly, you can choose whether or not to insert the associated components and features.
Everything.
Configuration Manager;
http://help.solidworks.com/2011/English/solidworks/sldworks/legacyhelp/sldworks/configuration/configurationmanager.htm
Smart Component;
http://help.solidworks.com/2011/English/SolidWorks/sldworks/LegacyHelp/Sldworks/Assembly2/Smart_Components.htm?id=65facb70bca7474c9493fecc11034df5#Pg0