As Grif and some others mentioned, backups are always essential, whether you've protected your system(s) with an UPS or not. But thinking you don't need an UPS because your system is saved is unwise, I feel.
Even in some of the ?professional? IT organizations I've worked, I've seen people make way too many bad decisions. For one, re-using the same media over and over to do a new backup is plain foolish. If you over-write your previous backup with the new backup you just started, what do you do if your system goes belly-up right in the middle of your save? Your previous backup has already been over-written and the new backup that just failed didn't successfully finish either. Translation: You've got nothin?.
Okay, so let's use the external hard drive backup method. You might date your backups, perhaps, and keep several older versions too. That may sound great because if the last backup dies for any reason, you've still got the older saves. Right? No, not exactly. You've still got a "single point of failure" situation because any power line anomaly that can kill your system can do the same to your external hard drive, too. Thinking that only the last backup set will be damaged is wishful thinking of the highest order.
Therefore, the way I see it, at the VERY LEAST, someone concerned about protecting their systems should do one or both of the following:
? As Grif suggested, have two external drives and alternate use of them. If one backup dies, the other drive will still have one or more earlier saves.
? Put your system and your external hard drive(s) on an UPS to protect them from all but the worst power line problems.
However, note that there are some cautiously-minded people (such as another well-known CNet Forum moderator) who'd scowl at just about any backup solution that involves use of hard drives, external or otherwise. To a certain extent, I have to agree. For some peoples? taste, a hard drive is entirely too volatile to be used as a backup medium. To suit some ?backup fanatics? (I mean that in a complimentary way), several layers of redundancy as well as having your backups stored at multiple off-site locations are the only backup solutions they?d ever accept.
Furthermore, if you?ve got a carefully crafted malicious script on your system, it?s just ACHING for more hard drives and networked devices to be attached to your system just so your saves can be destroyed too ... just like an underwater croc waiting for a thirsty animal to come to the water?s edge for a drink.
Yes, I know that off-site backups and extra redundancy seems to be going way over-board for the average home computer enthusiast, but it all depends on how willing you are to risk your data ... your tax returns, irreplaceable photos, music, videos, important documents, and who knows what else.