What is the main purpose for the grid in autocad? Who uses that Grid ?

In Electrical systems design, for example, it can be utilized to design thex cm square lights, instead of drawing a grid manually. 

The dimension and other properties of the squares of the grid can be managed to meet your exact needs. Also, the grid snap option has to be activated.

Some civil engineers, as another example, use the advantage of the grid in columns distribution. It can be utilized also as I think in clearly adjusting the scale of the work and to benefit the coordinates where needed. 

To enhancedrawing speed and efficiency, you can display and snap to a rectangular grid. You can also control its spacing, angle, and alignment. The grid is a rectangular pattern of lines or dots that covers the entire XY plane of the user coordinate system

Thank you for invitation,

Agreed with the previous answers.

The grid in AutoCad is used to help you dealing with a drawing that requires drawing lines and points in standard (similar)dimensions.

By turning (Snap) on, you can easily draw that kind of drawings, especially, knowing that you can edit the dimensions of the grid, so it 's not one grid imposed by the AutoCad. 

it makes you select snaping easily 

Thank you for the invitation

Agreed with the engineers answer

God grants success

This function to coordinate drawing

I normally used the Grids in AutoCAD for the CONCEPTUAL Drawings where proportions is more important than the actual dimensions itself. 

grids are point with coordinate   you can easily point coordinate 

Grid can be use for point locator easier. also architectural big drawing made in grid line easier 

GRID can be used to reduce the time of entering the dimension and we can selects dots to make a line circle or any other entity by counting dots