As essential as goals are to Google Analytics, it’s imperative to remember that they are not retroactive and that you should therefore set them up as early as possible in your implementation to begin calculating goal data immediately.
At a minimum, make sure to set up a goal for each submission or transaction confirmation page that you have included on your website (and that you’re not tracking with Google Analytics ecommerce).
If you have not designated your confirmation pages as goal URLs, you’ll miss important metrics such as conversion rate, abandonment rate (available if you associate a funnel with your goal URL) and $index (if you have specified a monetary value for your goal).
Don’t delay – set up your goals as a topmost priority.