Open a shop site and click a product. The address bar changes, the page changes, and nothing reloads. Visitors expect that smooth switch now, and it is what makes a single-page app feel finished rather than half built. Without a router, the usual workaround is a pile of state: a variable holding the current view, a switch statement rendering one component or another, and links that are really buttons wearing a disguise. It works for two pages, then starts to creak. The address bar never changes, so a visitor cannot bookmark a product, share its link, or use the back button properly. React Router closes exactly that gap, and the question is when it is worth adding.

What I would check before using it

My first check is how many views the app really has. One page with a couple of panels does not need a router, and adding one just adds a dependency to keep updated. Three or more distinct views is where a router starts earning its place.…