If this option is checked and the grid is crossing the assembly in the project, then Smart Assemblies will create a 2D family to represent the grid in the assembly view.
Example
Walls are crossed by grid lines in the model. This is a plan view of Level 1:
If we create an assembly with the Insert Grids option turned ON, then Dimension will also be turned ON in the Dimensioning Rules:
After the assembly has been created, you will get these results:
Front View - you can see the gridline 2D Family inserted with some available parameters and also the dimension line, in this case, from the grid to the wall.
Top View:
You can modify the Grid Family and use this option with different Categories, like columns, beams, etc. Here is an example of a column in the plan view:
