Trying to download a backup of a site recently, I found the siteTreeVersions table was over 80mb in size... which made it pretty much impossible to export and download from phpmyadmin. in the end i skipped in this table, and exported that table structure only.
this worked, but i'm wondering if anyone has a way of clearing the page version history, maybe just retaining the past 5 versions of each page. Working with old sites, this table can get huge!