Grid snapping is extremely important. Always work with grid snaps turned on. There are three grid snap options: rotation grid, drag grid, and scale grid. The following screenshot shows the Drag grid option, the Rotation grid option, and the Scale grid option at the bottom-right corner:
Uncheck/check: turns on/off the drag/rotation/scale grids. I would recommend always having this turned on. In some cases, for fine detailed work, you may need to turn it off.
[ ] Bracket keys increase or decrease grid.