Linens | Length Comparison | Square-Cut
As you've likely assumed, square-cut tablecloths are square. (Ta-da!) Using square-cut tablecloths on a round table may seem counter-intuitve, but there are definite advantages, the first of which is the price; square-cut are often the least expensive options for tablecloths. The second big reason for using square-cut tablecloths is that since the four corners touch the ground, once you have chairs in place they offer the appearance of a full-length tablecloth; and since the four flat sides are chair-height, you'll still have the comfort and ease of seating allowed by half-length tablecloths.
Much like half-length tablecloths, the major downside to square-cut tablecloths is in the appearance; some clients simply do not like the look of a square tablecloth on a round table.