Infinite gridlines activates the background grid to create associations between geometry. This helps reduce the number of dimensions necessary to support the entities of the design.
For example, by activating the Infinite gridlines (switch the option on in the Parametric menu), flaps that are the same height and right next to each other only require one dimension. The grid lines will make an association to all of the geometry that line up along that grid.
Deactivating the Infinite gridline tool (no check mark next to the tool in the Parametric menu) will require all of the geometry to be defined.