On top of what Leo mentioned you should actively check the logs to see if there has been any traversal query and if there is such query just create a relevant index. You can use Oak index definition generator for this purpose.
You may not have a "search" requirements yourself. When we mentioned "search" it does not imply a search feature or something like that. Oftentimes AEM needs to fetch properties/nodes to assemble and render pages and for doing this a query is built and executed behind the scene . We are referring to that search query. When there is a large number of nodes to traverse then performance issues may arise in which case creating an index would help to improve the performance.