If your site uses redirects, the redirecting page becomes the landing page's referrer. For example, if you've changed your site so that index.html now redirects to home.html, then index.html becomes the referrer for home.html. If someone reached your site via a Google search that sent them first to index.html, you won't have any data regarding the Google search.
For this reason, you should place the Analytics tag on the redirecting page as well as on the landing page. This way, the redirecting page will capture the actual referrer information for your reports.
Note that you may not be able to successfully implement the tag on all redirect pages as some redirecting pages may not have any code. Additionally, some browsers may actually redirect before the JavaScript call from the code can be made.
Related resources
Refer to Introduction to analytics.js to learn more about Analytics tag.
Refer to the Analytics (Universal Analytics) tag if you use Google Tag Manager to manage your Analytics tag.