Here you can access Smart Dimensions Configurations.
Checkbox allows you to select Smart Dimensions Configuration which should be used within Dimensioning Rules.
It's recommended to use Main Element Geometry tab to dimension cuts and openings and use Smart Dimensions for everything else. Read more about Smart Dimensions.
Edit - opens configuration window of Smart Dimensions.
Note: If you want to use Smart Dimensions, make sure it is also turned ON in the 'Dimensioning Priority and Notes' tab:
Read more about Smart Dimensions here.