In the preceding articles in this series, I have laid down some principles and discussed various options for migrating between Macs. You may by now have some clear ideas as to how to go about this, but the very best way to understand the process is to consider some practical examples.

In each case, you may have your own ideas, tempered by your personal experience and capabilities. There are no solutions which are absolutely or exclusively right, although some that are clearly not going to work out well at all.

Upgrading from an old to a new MacBook Air

Provided that your old MacBook Air (MBA) is running High Sierra or later, this is probably performed most easily by connecting them back-to-back using Thunderbolt and letting Migration Assistant do the shifting for you.

Before attempting this, knowing that you new MBA will be running Mojave, it’s a good move to bring the old MBA as close to that as you can. The only snag is that you could end up with the old one running 10.14.2, and the new still on 10.14.1, and may find that migration during setup is refused because of that. Don’t be surprised if the new MBA decides that it needs to be updated to 10.14.2 first, then once that’s done you can run the Migration Assistant app from /Applications/Utilities.

There is a wrinkle you can use to make this easier. When you create your first admin user account during setup, use the same username, both long and short, and the same password as on your old MBA. This will encourage Migration Assistant to offer to merge the first admin user account from setup, with the migrated items into a single account, which is almost certainly what you want it to do.

If your old MBA is still running Sierra or earlier, then be very cautious as to what you migrate, at least during setup. Although old settings and components may not actually be incompatible, they could easily waste a lot of your time fixing things on your new MBA which get broken by what is migrated.

If you’re not going to let Migration Assistant help, or only allow it to move your apps, perhaps, it’s worth making a clone of the startup volume in your old MBA to external storage, and using that as your source for moving documents and other items in slower time. This frees up your old MBA for repurposing.

Laptops also typically have smaller internal storage, and you may well need to be very cautious about what you migrate or copy across from your old MBA. If you’re getting rid of the old Mac, after making its last backup and any clone, have a really good housekeeping session so that you only have on it what you want to carry across to your new MBA. It’s much better to do that before migration than struggle afterwards when you end up with very little free space on your new MBA’s storage.

Upgrading from an old iMac to a new Mac mini

Be cautious when considering whether to let Migration Assistant perform tasks like this. Although macOS should cope with the great differences in hardware, your setup will differ considerably between the two systems, particularly if your iMac isn’t on Mojave. You should get away with just migrating your apps and possibly Home folder too, but letting macOS migrate much more than that may well end up with unwanted and irritating items and settings on your new Mac mini.

Once again, being a recently-released model, you can expect your new Mac mini to be running 10.14.1 or later. A good plan might be to set your mini up as a new Mac, update it and ensure that you’re happy with its configuration, then run Migration Assistant to move across just the apps and other items which you need on your new system.

In this case, trying to clone your old system onto the internal storage of the new mini is likely to lead to disaster. Remember that your new Mac now has a T2 chip: although good cloning apps like Carbon Copy Cloner and SuperDuper will handle that fine, it’s too easy to end up with old settings, extensions and other components which may make your mini rather unwell.

If you’re intent on performing a fully manual migration, by all means use a copy of the startup disk of your old Mac, but be very wary about what you copy across to the new mini. You also don’t want to touch anything protected by SIP, or on hidden volumes like the Recovery partition, as those are very specific to the Mac mini.

Also note my advice about Thunderbolt 3 to 2 conversion below, as your old iMac is likely to have Thunderbolt 2 ports, and your new Mac mini has Thnderbolt 3.

Upgrading from an old iMac to a new iMac Pro

This might appear to be one of the simplest migrations, but take it from me that it may prove far more complex than it should be. Those now buying new iMac Pro systems are likely to receive a Mac which has not got Mojave pre-installed, but High Sierra 10.13.2. Assuming that your old iMac is now running Mojave, migration during setup won’t be allowed, and there isn’t any straightforward way to upgrade to Mojave until you have completed your iMac Pro’s setup.

Worse, you may not confirm this problem until you have already had to set up the first admin user on your new system.

Allow plenty of time, set that first user up with the same names and passwords, and then let your iMac Pro connect properly with the App Store in High Sierra. If you already have a copy of the current Mojave installer, you can copy this across to your Applications folder. You can also copy across an earlier Mojave installer and all subsequent updates as standalone installers.

Whichever way you choose, your next task is to bring the iMac Pro up to the current version of Mojave. Once that is done, hook up your old iMac, preferably using Thunderbolt with the Apple Thunderbolt 3 to 2 adaptor (as required), back to back. Then open Migration Assistant on both Macs, and let it move across as much as you wish.

If your old iMac is running the current version of Mojave, my experience is that you can afford to migrate as much as you want, including the system configuration. The only thing to be very cautious of is keeping free space on the startup volume of the iMac Pro: if (like me) you are moving from a 2 or 3 TB internal Fusion Drive to a 1 TB SSD, you need to make careful provision for how to fit the quart into a pint pot – the subject of the next article in this series.

One other important issue to plan for is that the Apple Thunderbolt 3 to 2 adaptor doesn’t supply power to external storage, and I haven’t found an equivalent adaptor which does. If you have a Thunderbolt dock, that may well offer an effective route between Thunderbolt 3 and 2 with the supply of power. Otherwise, you’ll only be able to connect external Thunderbolt 2 drives which have their own power supply.

In the next article in this series I’ll look at how to cope with downsizing your internal storage, such as going from quite a full 2 TB boot disk down to a 1 TB SSD.

Apple has a series of articles which provide basic advice on migration to a new system:
Set up your new Mac
How to move your content to a new Mac
Restore your Mac from a backup
OS X: Manually migrating data from another Mac