why back up a Mac

Belt and suspenders. It's always good to have more than one type of back up. What if Apple's servers are down when you need to access a back up? What if your internet connection isn't working? What if, heaven forfend, your iCloud account gets hacked? Those are just the things I can think of off the top of my head. It is, however, still a choice.

Best of luck.

As long as there's plenty of available of iCloud storage space for backups, there's no need for an external drive.

Manage your iCloud storage - Apple Support

Meg St. Clair does bring up a good point if there are problems restoring from a backup due to an internet connection glitch or Apple servers are down but that would be rare.

You can check iCloud system status anytime here > https://www.apple.com/support/systemstatus/

This reminds me of the blurb Carbon Copy Cloner in test mode puts up: Total system failure and disk loss, how long before you're back up?

Supposing you've a 512GB MBP@80% full, how long before a reliable download of all your junk finishes? On an external drive, we're talking of ~2-3 hours or less with 100% certainty.

I love iCloud for accessing files across multiple devices. I'm less crazy about using it for back up. Yes, it's how I back up my iPhone and iPad. And the braindead simplicity of it is great. But, it was a great deal longer than 2-3 hours before everything was back on my iPhone when, for unknown reasons, it simply erased itself a couple of months ago. And that was just a 64 gig phone.

The fact that you have a back up strategy of any kind puts you light years ahead of way too many people!

Best of luck.

iCloud is going to back up about 5% of the files on your Mac.

You will not be able to restore your Mac to the same state from your iCloud backup. Your iCloud will only restore the few documents that you happen to store there.

Each has its place. I don't use iCloud for backup as such of my Macs (but I do for iOS devices). What I DO use for syncing and backing up:

• iCloud sync for iWork documents that I want to share with mobile devices
• iCloud sync for Contacts, Calendar, Bookmarks
• Dropbox.com sync for files that I share between computers and with other members of my team and my clients
• Box.com sync for clients that use it
• Google Photos sync for all photos
• iCloud Photos for saving photos taken with my iPhone (which also automatically get uploaded to Google Photos)
• upthere.com syncing for photos, music and documents (because I'm a beta tester; otherwise it would be redundant)
• livedrive.com backup, which backs up all changed files on my computer hourly, keeping the 30 most recent versions of each file
• Evernote, which syncs all of my notes across all devices (4 iOS, 3 Macs, 2 Windows) and also has web access

In addition to all of the above, I have two Time Machine external drives on my MBP, one on my MBA and one on my wife's iMac. All of them are dual RAID configured mirrored drives, so each one has built in protection against a single drive failure. Time Machine offers a critical service that none of the other backups have; If I have to wipe and restore a drive in any computer (or get a new computer), when I run the install procedure it will automatically restore the entire disk file structure from the most recent Time Machine backup, so I don't have to think about the details or wonder about the best place to restore each file from.

So your hard drive dies - it happens. Or the computer is stolen. That happens too.

Question 1: is all your data in the cloud? Every bit of it? What about your FireFox or Chrome bookmarks? Your playlists? What about all the configuration you’ve done on your computer getting the desktops set up and frequently used words added to the dictionary?

Question 2: where are your applications? Oh, they aren’t in the cloud are they? Do you even remember all the applications you’ve downloaded and installed?

Question 3: Do you really trust iCloud (or any other service) to be there exactly when you need it?

Question 4: Do you have any idea how long it is going to take to download all those files and applications? Hope you don’t have anything planned for the weekend and I really hope you don’t have a report that needs to be turned in the next morning.

With a clone backup if your hard drive crashes and you have an emergency situation you can be back to work with minimal data loss in minutes. With a TimeMachine backup you’ll have to wait a while but TimeMachine, if kept connected to your computer while you use it, gives you more up to date backups.

Sure, a service like iCloud is better than no backups at all, but it is like a leg splint made from a tree branch - better than nothing but no substitute for a cast or medical boot.

On the issue of how long it takes to recover, if you opt for an external SSD, then recovery times might be measured in minutes instead of hours.

Sometime ago I helped a colleague migrate from an Air to an MBP. Both had SSD storage: 256GB on the source (~190GB occupied) and 512GB on the destination (empty save for the from-factory OS, ~20GB or less). Source in Target Disk Mode (essentially, the old Mac behaves like an external drive), connection via Thunderbolt cable, destination in Setup Assistant's Migrate option (essentially, a full disk restore minus the OS). Grand total of ~170GB, including apps, documents, settings and user accounts, flew across the wire in less than 30 minutes.

In security parlance, it's all a matter of risk assessment. How much are you willing to pay today vs. how much are you willing to pay tomorrow. Cost today might mean a few more coins invested in drives, cost tomorrow might mean the price of losing irreplaceable data.