Patent search for non-marketed inventions

A patent search can reveal the LACK of activity (blank space) which is useful to identify "Freedom to Operate". The other angle to interpret it is that it is a public source for business intelligence, some inventions are used for internal purposes and may reveal hints about intermediate R&D outputs. There's also specialist search engines which correlate issued patents with employment to identify key personnel which is indicative of market potential as it can take years for (traditional) product development. So necessity depends on whether the cost of negative information is worth it (looking for lack of competition). Note that a lot of IP is in trade secrets so a patent search in isolation may give misleading results.

Not at all - and quite to the contrary. What is the purpose of your search? Are you interested in obtaining patent protection yourself? Then you need to know if any patents have been granted or are pending as published applications, so as to determine what the probable patentability of your invention is. In a similar manner, are you intending to market your invention? If so, then you want to know if there are any patents or pending published applications where you may infringe one of the patents or the published application if the application eventually gets granted as a patent.

No, you should still do a search. Just because you do not see it on the market does not mean it isn't being produced. You would not want to spend time and money doing prototypes on something that has already been patented or at least applied for. The search might also help you refine your own idea and make it better.