The blocks, wires and groups on the canvas always snap to a grid. You can decide whether the grid is to be shown or not. The grid is not shown by default. When you zoom the canvas, the grid is zoomed accordingly.
The toolbar button always indicates whether the grid is currently hidden or shown. When the grid is hidden, the button looks as shown above. When the grid is shown, the button looks as follows:
.
If the model is in the Active state (read-only mode), it is not possible to toggle the display of the grid and this button is therefore disabled.
To show or hide the grid
Click 
in the toolbar of the model editor to toggle the display of the grid.