What happens if I don't update my theme?

There is a detailed post explaining how you can avoid editing theme files. Of course, this alternative predates child theme support in Suffusion, and child themes work perfectly well (and more flexibly).

What would happen if I just decided to never update my theme?

I don’t know. If there are features in a new release that help optimize/speed up things you will lose out on those. You can subscribe to the announcements feed from the link above, then decide if you want to upgrade or not, after reading the release notes. In general it is better to keep your theme edits to a minimum and do an upgrade when available – every release of Suffusion has had significant changes so far.

Thank you Sayontan, I did a little more research on creating a child theme and still found it difficult to understand, but I went ahead and updated Suffusion on my blog anyway and it did not get rid of all of my formatting!

I updated too & didn’t lose any formatting ??

Options of the theme are stored in the database, unless you have edited theme files to do your formatting. That is why updating the theme preserves the options.