First off, the laminate is usually required by the Flooring Manufacturer. Reason being, if their product is installed on an 'uneven' or damaged substrate, their product will 'fail'. The underlayment create s smooth, flat surface for the laminate.
Secondly, the key to almost any flooring is the subflooring and the 'system' it sits on. From this standpoint, the underlayment doesn't add anything when it comes to support.
A laminate is usually installed perpendicular to the subflooring immediately below it. In some respects, this will help strengthen the floor as opposed to installing it parallel to the subfloor. But don't be misled - In short, the laminate is to protect you, the installer, and the flooring mfgr. when it comes to a laminate flooring.
PS: Oh, I'm making a big assumption here. When you say laminate, you are referring to vinyl and not something like Engineered Hardwood Flooring, right??!