To toggle the display of hidden lines on or off press the K button on your keyboard. At times, hidden lines will allow a better visualization of the piece as well as save you some time from hiding items that may not need to be hidden. The first example here is using hidden lines in conjunction with intersecting faces to make mortise and tenon joints.
This is a previous design video but it will show you an example of using hidden lines to speed things up a bit. The video should start where hidden lines are used.