[AT&T, Rogers, Bell, Telus Samsung Galaxy S III] PeterGuru:
Good question ...

Good question!

The vast majority of custom ROMs do not use the DATA directory to install apps. While it can be done, it's not common practice to do so. Also note that I have yet to see a stock ROM that installs anything to the DATA directory. Stock ROMs have everything installed in the System/App directory, which is completely erased when you flash a new ROM.

Usually, the only thing that's in your DATA directory are apps that you've downloaded and installed from the market. However, and this will interest you, whatever apps are in the DATA directory are removable via the standard uninstall feature. ONLY System apps cannot be removed this way. Yes, they can be removed, but it's a more complicated procedure.

The whole idea here is, if you want to flash a new ROM, go ahead and do so knowing that all device files will be new (from the new ROM), but you will ONLY restore the DATA folder by using the Advanced Restore feature. To repeat, even if there's an app within the DATA directory that you don't want ... you can very easily uninstall it through Settings>Application manager>Downloaded, by simply selecting the app you don't want, and then pressing the Uninstall button at the top right.

The entire advantage to using the DATA restore function is to very quickly (and I mean VERY quickly ... about 2-5 minutes) re-install ALL your previous DATA apps and, most importantly, keep all previous settings intact ... including all previous SMS messages and Call Logs. When I say that it keeps your settings intact, I mean that, for example, if you had an app such as Twitter previously installed, and you had it already set-up with your account name and password, including whatever sound you had already selected for notifications, and any other settings, ALL THOSE SETTINGS would be automatically re-established. This can save a tremendous amount of time.

Peter

P.S. Time for bed. It's 12:39am here in China. Will be home again in about 3-4 weeks.

Addendum: Okay, I'm still awake. I wanted to mention one more thing: Tibu is a great backup and restore app; however, all it really does is perform the exact same function as the DATA restore feature. There are two things to keep in mind. One, Tubu is a 3rd-party app, which means that it has not been specifically designed for YOUR device. It's designed for use with many, many devices, so it's potentially not 100% compatible (case in point ... I don't use Tibu anymore because it caused too many little glitches over the last couple of years). Yes, it works well, but in order for you to restore apps and settings, you have to do so when your device is powered-on and back to the home screen. The time it takes for Tibu to do it's work is much longer than it takes for the DATA restore to work. The whole idea here is not only saving time, but being about as confident as you can be in knowing that your restore is being done in a manner thats 100% compatible with YOUR device. Using the DATA restore method ensures this because it's simply taking exactly what you had before, what was working perfectly before, and re-establishing it. Two, when speaking of speed, keep in mind that, like your PC, if you want to do a complete defragmentation, it's enormously faster to do so BEFORE the operating system loads. Once the operating system loads, certain functions take much longer to complete when compared to doing the same thing in what I'd call DOS mode ... or the mode your computer is in BEFORE the operating system loads. Similarly, when using the DATA restore function, you're effectively restoring all apps in the "DOS" or "ROOT" mode of the device, rather than waiting for it to load it's operating system, and then doing the very same task via Tibu. Question: If you had 100 apps to restore in Tubu, how long would it take? For me, restoring 100 apps via DATA restore takes about 2-3 minutes.