We don't know what's been lost because they were kept secret. The patent, being a publicly accessible description of what was accomplished and how, increases the understanding by anyone who reads it.
Let's take Google's PageRank as an example.
Until PageRank, search engines tried to decipher the content of a page to decide the value of that page in a relevant search. PageRank took the value of page links as THE defining metric of quality and the result was a much better search engine.
Had Google kept this a trade secret, we'd still be guessing at how they accomplished the goal. Knowing what they did, and how they did it, means that the knowledge is available to everyone.
For a non-search related project we are doing, I directed on of our team members to read the PageRank algorithm, as it is somewhat informative of a potential solution to one of our problems.
Google patenting PageRank has meant that we get the value of knowing their process, but are unable to use it to compete with them.