Scott Hanselman’s rationale is excellent. I don’t follow all of it but the post and the comments following are all worth reading.
If you don’t back up your computer or your mobile devices you’re looking for trouble, simple as that. Hard disks fail and short of that, operating systems fail.
What I do:
1. I have two external bus-powered, small, portable LaCie firewire 800 drives that I use SuperDuper! with to back up my entire computer.
On day 1 I use SuperDuper! back up to drive 1 and put it in a fireproof box in our basement.
On day 2 I use SuperDuper! to back up to drive 2 and when it’s done I take it to the basement and swap it with drive 1 which comes back up stairs and goes in my desk drawer.
On day 3 I back up over drive 1 (using SuperDuper!’s “smart backup” to just update the new stuff, etc.), then take it to the basement and swap it with drive 2 in the fireproof box.
I repeat this daily, even if I don’t use my computer for anything significant. This way I don’t think about what’s backed up when, I just know that the most I could lose is a day of work.
2. At the same time I’m doing my SuperDuper! backups I’m doing twice a day Time Machine backups onto another LaCie external hard disk (a bigger one to hold the growing Time Machine collection of days).
3. The only cloud backup I have isn’t really backup, it’s iCloud and it’s just my contacts, my email, my calendar, and a few other things. I use gmail (cloud based) and have a .me mail account (cloud based) so my email lives outside of my house.
I’ve been using this method for years and it’s saved my bacon numerous times.
The important thing to consider in both backing up and in deciding which methods you want to use is this: If your computer dies or is stolen, how fast can you be back up and in business. My SuperDuper! cloned backups will boot any modern Macintosh and so, all I have to do is boot my wife’s MacBook Pro with the most recent of my backup drives and that computer is essentially mine with all of my stuff exactly the way it was when I backed it up. Then, I can go to an Apple store, buy a new MacBook Pro (or have mine fixed if it’s fixable) and use SuperDuper! to backup back over it, or, leave the new native system on it and migrate all of my stuff back.
There is no perfect method for doing this stuff, the important thing is to do it and work out a method that works for you and that you’ll use on a regular basis.