Backing up a site's database and files should be a regular routine for your maintenance.

Usually Xoops sites run perfectly well once they are set up and running, but there is never any guarantee that your server will function without fault and maintain all the data. This is even more important if you are using a hosted server. Servers can go down, suffer malicious attacks, or simply are managed badly by some hosts. Severe weather can cause power-outs and data damage.

When you are carrying out any site updates, module installation, hacks, core updates, themes, or other major arrangements on your site, there is always a risk that things might go wrong.

Take nothing for granted and BACK-UP regularly and especially before any changes to your system as above.

Database: If you are running a commercial or busy site with lots of interactivity you may want to back up the database on a daily basis, keeping at least a weeks worth of back-ups in reserve. Other periods are weekly but not less than monthly. You have to acertain the risk of loss and value of your material against the maintenance time involved. Backups are like a parachute ... you probably will never need it, but if you do, you need it realy badly!

mainfile.php: This is perhaps the most important file on your whole site. ALWAYS keep a back up of this, probably on removable storage in a safe place.

Xoops files: This is relatively easy as they are probably situated on your hard drive. However, it's important to back-up a server version of these. This means any online configurations that are written to your files by the system, plus any hacked versions. Its also useful to make a note of any chmod settings. I personally download the whole of my xoops files off the server, thus keeping the distribution and configurations. Then make small text files in the various modules to remind me of any settings I may need to make if I need to reinstall.

Passwords etc: It's obvious, but easy to forget how important this is. Login details both for your own admin, site database, user permissions, cpanel login etc.

You may want to consider automating the back-up process. Some applications will do this on a timed basis and email you the back-up files.