The crop tool can add composition overlays to your image. Click the overlay icon to view, and/or press the letter "o" to cycle through the overlays. You may find that you have to adjust the crop slightly for the overlay to be visible.
The crop tool is great for straightening horizons, too. Click the straighten icon then click and drag along your horizon to level it.
By UNchecking "delete cropped pixels", your crop is non-destructive.