What are patents for is a question that may seem simple to answer, but the use of a patent is difficult to put down.
Essentially they are a monopoly, a protective right. Which may be considered a positive right.
But they also have a negative power. By definition a monopoly excludes ourselves, so is negative for everyone else.
Patent trolls are the extreme of the negative side of patents, where a company with no other interest than owning patents in order to enforce them might buy up job lots of intellectual property rights (IPR) in order to sue or obtain licenses from others.
These IPR might be designs and/or trademarks but are most likely to be patents.