If you run a new website there is most often a small amount of content at its start. But later the content is growing and users may get an issue to find the content they are looking for. That’s the time when a good build in live search is needed latest.
But it would be the best solution to have such live search already implemented before you go live with your website. And if you expect your website to grow fast you need a very capable live search.
I created such a website together with a service provider for the LibreOffice extensions and templates repository. The site is build on Plone with some add-ons. The Plone Content Management System (CMS/DMS) already provides a build in fast live search. The search is already running by default. There is no need for another implementation of a live search or search function except possibly very big or special environments. But for such cases there are add-ons available in the Plone add-on repository to get e.g. Apache Solr integrated within your Plone installation.