Which is better for the long-term health of my database?

Without doing changes in your settings, there is no need to touch either of these.

That is not correct.

I never change the configuration and I routinely encounter situations where link addresses do not work properly unless I update or purge.

For example, I just created a section and category that is fed by rss. I then created a menu link to each. But when I type in mysite.com/category-name/blog I get a 404. Purging will correct this problem.

I'm not really wondering what situations lead to this. I encounter them frequently and know what they are. I just simply want to know which option is better - update or purge?

I have the same problem.. without changing any thing.. the url can change or stop to work.. if I purge them then they work just fine..