Lemley on licensing
A commonly offered justification for patent trolls or non-practicing entities (NPEs) is that they serve as a middleman facilitating innovation, bringing new technology from inventors to those who can implement it. We survey those involved in patent licensing to see how often patent licenses actually led to innovation or technology transfer. We find that very few patent licenses from assertion actually lead to new innovation; most are simply about paying for the freedom to keep doing what the licensee was already doing. Surprisingly, this is true not only of NPE licenses but even of licenses from product-producing companies and universities. Our results cast significant doubt on one common justification for patent rights.
There are situations like the Selden patent (application filed in 1879) wherein licensees gain no insight from the patent.
There are different cases wherein the licensee takes advantage of the knowledge without expanding upon it.