Website speed and page load time is definitely a driving force behind your website visitors behavior that directly define the success of your business and online store sales.
Lets take an example of Walmart. When they found out they were not the fastest retail site on the internet, compared to EBay, Amazon etc., they have decided to overhaul their site speed.As a result: For every 1 second of improvement they experienced up to a 2% increase in conversions. For every 100 ms of improvement, they grew incremental revenue by up to 1%.
Search engines routinely fall back on pages load time in their rankings, as they assume the responsibility of optimal search results. Favoring fast sites over slower ones, a search engine meets the main goal of keeping customers content with the results delivered.
This is where Magento website performance is really crucial as it is what drives conversion rates and brings revenue for online businesses.
The principle applied with Full Page Cache follows a common pattern. When a user visiting a website page for the first time, Magento generate and deliver this page to the visitor and automatically save a copy of it to the cache (cache storage). Then all those pages just get stored in a cache. Each subsequent time when user request arrives, the system does not does not request Magento to generate a page, but returns the cache copy of the page from cache.
This greatly reduces database and server load. Once the server generate a page it does not need to generate it again and again, it simply returns only cached copies - immediately. An extension is significantly increase the load speed of Magento store.