If your site has over 20 pages, a good internal search within a site is key, according to the good ‘ole people at Yoast. You’ll want to make sure that people can find the information they seek and find it fast, which means giving them an internal search option to try before getting frustrated and leaving your site. However, there are ways to better design or place your search fields as well as optimize your search results pages that you need to pay attention to.
Another benefit of having a good internal search option is that it provides valuable data for optimizing your website. Did you know that Google Analytics tracks the keywords your visitors type into your search (via Behavior › Site Search › Search Terms), thereby giving you the opportunity to improve your content by providing them with a better result? So check those keyword search results yourself and give your visitors exactly what they are looking for, even writing new content if you have to. Learn more about internal site search AND search options for online shops with this wonderful well-written article by Yoast:
Internal search is the search option on your own website. It’s, for instance, the search widget in WordPress and the product search in WooCommerce… If your website is packed with content, you’d really want to add that internal search option. When someone lands on your website from Google, for the most part, they are looking for a specific piece of information about a certain subject. If they can’t find it immediately after clicking that link in Google, there are only a few options to prevent that user from clicking back to Google immediately.