How often should you back up files?
Daily weekly monthly ?
When there are important changes/additions that you do not want to lose.
A disk image backup is simply wonderful anytime there is some problem (disk went bad, or system went bad, etc).... You can restore and be back up running in maybe 15 minutes, and be same as before.
But you will lose any changes made since the backup was done.
So my notion is there are two philosophies.
1. Backup anytime you realize significant changes have occurred. This would normally NOT include stuff like Microsoft updates, which are always available again.
2. (My plan) I use a batch file to copy later dates in a few important data directories, to another disk. I run that anytime there are significant changes to that data, which is normally at least daily (it is just one click, and only copies the newer stuff). Then I run system image backup every week or two. In the event I do restore with older data, I also have the latest changed data elsewhere.
System backup has one standard risk. If you backup by overwriting the same backup file every time, then you may backup any problem too, before you realize you have a problem. Restore simply restores the problem then.
So, you need a plan that will retain your previous backup too, so if you realize your backup was corrupted, you still have an older one to try. You manually delete the old ones them,
but always keeping the last two or three. Never overwrite your only backup.
And I say a Disk Image Backup. You cannot backup the system by just copying files somewhere. That will not be bootable. To have it work at all, you would have to reinstall the operating system and all the programs, so a copied system is worthless that way. So instead, the great solution is to buy disk image backup software (very inexpensive, runs in background while doing regular things, no big deal to do).
You could just copy photos or data files, which is important, but it will not backup the system with a bootable usable version. Sooner or later, there comes the day your disk fails, and will not boot. This can be catastrophic, it is ALWAYS at the very worst time. Tomorrow morning, stop and imagine, what if it is all gone, and will not boot up today?
But if you have a recent system image backup, you just bolt in a new disk, and run restore (from its bootable CD), and you are back up and running in maybe 15 minutes.