The combination of these two modules gives you full search capability within the context of your site. In other words, without having to define how searching should be done, using these modules you can specify that it must be done and edit the output format of the search results.
Having this functionality on your website will ensure that users can easily find the information they are looking for (on your site) and that they are presented with any related information (on your site) timely.
Whether you have a small or large website (and independent of how the information is modulated into different pages) you will need a search capability to ensure a better user experience. And because this module handles what could previously have been seen as a difficult function to implement, there really is no excuse not to incorporate searching into your website.