That is especially so for these floors since the installation technique is usually a floating floor. That means the pieces click together to form a mat and then hover over the subfloor with no glues or nails needed. Since they aren't affixed to the subfloor, it is the underlayment that will provide the foundation and give stability.
Underlayments also insulate from noise and provide cushioning when walking or standing. Sometimes a vapor barrier is also needed since some subfloors (namely, concrete) can be damp. Since the material is composed of wood products, it will be affected by humidity.
Many come with pre-attached underlayments. If yours does, no need to buy an additional one. If, however, yours doesn't, it's strongly recommended that you select the best one for your floor. Your flooring expert will advise you.
For more information about laminate flooring visit the Floors For You Kitchen & Bath showroom in Jupiter, Fl. We serve Jupiter, FL, Palm Beach Gardens, FL, West Palm Beach, FL, Juno Beach, FL, Hobe Sound, FL, and Boca Raton, FL. Ask about our estimates