Do you mean beneficial to search ranking or just overall beneficial? Because it is obviously good that the website's readers can navigate the site easily by searching and that you can make money from the ads displayed on the search page, for example, using Google custom search.
it will help users to find your site content easily, and help you to earn some pennies with adsense..
yes it is beneficial to both - the user as well as webmaster. visitor can quickly search for anything he is looking on the website and as a webmaster you will be having loads of data with you about what people are searching on you website and you can optimize the site accordingly.