Also premature wear to the inner hearth might occur. If you don't have a grate, take measurements of the inner hearth's depth, width in front, and width in back. Go to your local stove shop and pick one out. A heavy cast-iron grate will last much longer than a grate made of welded steel bars. If you plan to use the fireplace often, spend a little extra for a good cast-iron grate.
Some people use andirons in place of a grate.
But as logs burn down, andirons will no longer hold the logs up. They will collapse to the floor of the firebox. So even if you have andirons, a grate is still a good idea. You can keep the andirons for decoration and ambiance. Just slide the rear legs under the grate, or put one on each side if they are too tall to fit under.