The good thing about over-ride: what if you have more than 1 templates and want to switch back and forth? And the default template is always there so you can fall back any time in case some thing happens.

Now if you want to use svn for your site, I don't see any problem with that, as long as you know what you are doing. And I'm not saying that svn is extremely hard, it's just a bit difficult for non-tech people, and a bit complicated (you have to get a svn server to, there are lots of free ones out there though, but it still mens more work). Always remember, the users do NOT like more works, I have just said goodbye forever to DELL because they simply gave me more work, required me to call their support staff while I don't want to.