With the exception of concrete, both resilient and hard-tile products will require an additional underlayment specified by the manufacturers. With regard to the hardwood flooring industry, engineered products that are installed over a wood-type subfloor with an adhesive normally require an additional underlayment to establish a smooth and flat surface.
In today's ever-changing construction industry, the importance of a qualified underlayment and/or subfloor remains paramount in the eyes of the hardwood flooring industry. New construction has always been considered cut and dried in determining the suitability of the subfloor. Yes, there still may be challenges in floor preparation, but at least they are exposed upon your arrival at the job site. On the other side, the remodel/replacement market may reveal your very own fear factor once hidden subfloor inadequacies are exposed.