Suppose use have enabled the "Track page view statistics" from dashboard System & Settings and it stores a lots of data into statistics table. After a year or two, your database size will be 300MB or more. Now you are trying to backup your database. And somehow you need to restore it. Or you need to create a duplicate copy in another server or localhost. The problem will arise, as the big database will not be imported very smoothly. You need to search google for solution to import big sql.
But there is an alternative way. If the statistics doesn't matter to you, you can flush it before having database backup. It will reduce the sql size a lot.
If you are not aware what you are going to do, just leave it. This add-on might not for you.