The vast majority of patent information is never disclosed or published elsewhere. Patents contain a wealth of specific technical detail, research data, and drawings. Patents and patent applications often contain information on new advances long before that information is published in a journal article.
If you are a researcher, particularly in the applied sciences, being aware of the relevant patent literature can help you evaluate your findings even if you do not intend to file a patent yourself. Patents can be a link between academic research and industry research, which often does not get published in journals the way academic research results do.
If you are an inventor, you should be aware of relevant prior art relating to your technology.
If you are an entrepreneur, you should monitor your competitors' new products, and where they are patented.
Because patent documents contain highly technical and oftentimes obfuscating language, it can be difficult to locate relevant patents especially if you do not know the patent number or inventor's / assignee's name. Keyword searching alone will only get you a small part of the full scope of patent documents related to a particular topic. Happily, modern search tools are making it possible to search for patents much more easily.
Keyword searching is probably the most familiar search strategy, since this is typically what we use when searching for other types of documents. Finds patent documents containing the word(s) you entered, and sometimes common variations on those words.
This involves searching for the person who invented the item being patented, or who has been assigned the patent rights. The assignee can be a company, not just a person. The inventor can waive their right to be named in the patent document, so this is not a foolproof method even if you know the inventor's name.
Precision searching using a patent classification system, typically Cooperative Patent Classification scheme (CPC). These systems organize patents hierarchically based on what they are about or for. If you know the classification for the type of item you're interested in, you can quickly locate all patents for that type of item regardless of language used.
The USPTO defines a patent family as "the same invention disclosed by a common inventor(s) and patented in more than one country." Patent family information can help you track down additional relevant resources by locating additional patent documents, other items citing those patent documents, etc.
Contact your librarian for more help with patent searching. A librarian can help you develop search strategies, navigate a CPC search, and more.
If you are considering patenting an invention and require an absolutely thorough search for existing patents, your best bet would be to get in touch with a patent attorney.