If you use one of Full Page Cache Extensions, then it’s extremely necessary to add a Magento Cache Warmer / Crawler to your e-commerce store. Such extension will crawl your site to ensure that all the pages provide the fastest load time. Warmers and Crawlers also refresh old cached pages. As a result, your visitors get the most relevant content and the fastest speed. This type of Magento extensions often relies on special techniques designed to reduce bandwidth and CPU usage.
Cache Warmers / Crawlers are also used to improve cache hit rate of a website – the ratio of cached and uncached requests. Sites with the higher hit rate are always faster (combined with a fast cache solution, of course). The Full Page Cache Crawlers / Warmers solve this by pre-caching uncached site pages. As a result you get more cached and less uncached requests, which increases the cache hit rate.