Google Analytics is an SEO factor in search engine optimization. If you check website SEO rank, you will see the result required Google Analytics. So you should Setup Google Analytics to your website for best result. Google Analytics not only helps to increase SEO score but also helps to optimize keywords. It collects details about website traffic and keywords information. In future, you can optimize your website using those collected keywords because it already ranked your website. After using those keywords your website will be in the first page of google. Bye the way don't forget to add google webmaster tools to Google Analytics.
You may use google tag manager to add Google Analytics code to your website.