Note: many stores do not need addons. If you need an addon later on you can purchase it at any time.
The Deep Crawling / Logged URLs will help ensure that deep catalog pages (page 2, 3, 4, etc), sort options (sort by price, bestseller, etc), layered navigation filters, and more are crawled. The end result is that more pages will be crawled, which will make your store faster to end users. This addon requires the use of the Extendware Full Page Cache extension.