[Desire HD Android Development] sashank:
About dirty flashing -

To everyone with questions about dirty flashing - I dirty flashed SR12 over SR11, I've been dirty flashing since BR11 actually. No problems at all. Just had a Facebook FC on SR11->SR12 which was fixed by clearing data of FB. You don't need to post over and over again asking about dirty flashing. Every time there's a new update out there are countless posts asking whether it's okay to dirty flash. It IS ok to dirty flash. It's not rocket science. When you flash a ROM, the /system partition is formatted, new ROM is written to it, and any gapps/mods you flash over that. There is no mixing of new ROM files with old ROM files, because /system is formatted first before flashing a ROM. Sometimes FCs and other problems occur because of conflicting/incompatible user apps in /data. If that is the case for your phone, then do a clean flash. Many of us know exactly what is in the /data partition, and what to fix if there are errors, so we don't have any problems. If you're having constant FCs on a dirty flash, then clean flash. First and foremost, if you want to know if a dirty flash works fine, then please try it yourself! Make a nandroid, dirty flash, and see for yourself if everything is fine. If it this, then good for you. I don't understand why so many of you ask the same question "is it okay to dirty flash?" over and over again for every new ROM update.

1) Yes, it's okay to dirty flash.

2) Try it yourself. There's no need to ask others how it goes. Do you ask another person to taste your food before you eat it?

Clean flashes are usually not necessary for minor updates to the same Android version like 4.2->4.2.1->4.2.2. There aren't that many substantial changes between minor versions to require a full data wipe. You SHOULD clean flash between major updates such as 4.0->4.1, 4.1->4.2, as there a LOT of changes. Taking CM as an example, if you flash CM 9/10 over CM 7, you'll have a ****load of FCs and other problems. If you flash CM 9.1.0 over CM 9, that's fine. cfX 4.1.2 -> cfX 4.2.2 requires clean flash. cfX 4.2->4.2.1->4.2.2 doesn't require it, although there's no harm in doing so if you have the time.

That said, the reason many people ask for full wiping while testing ROMs is because there can be certain problems that are user data related. Debugging is hard work for devs, and it gets complicated when where are user introduced problems. To be on the safe side, users are asked NOT to report bugs without clean flashing. You can dirty flash all you want, and it'll work fine most of the time, good for you. Just remember not to report any bugs if you haven't clean flashed. Clean flashing means full wiping and just flashing the ROM, and checking if the problem exists. You're not supposed to restore any data.

Full wiping + flashing + restoring apps and app-data through Titanium Backup != Clean flashing

You might as well dirty flash if you're going to do that, no difference. If you want to contribute to ROM testing, then full wipe, flash the ROM and check for the problem. If it's regarding an app, re-install only the app in question and try. That's all there is to it. Dirty flashing isn't magic. Read the update changelogs and use common sense to decide how major the changes are to warrant a clean flash. There's really NO need to have posts upon posts asking whether it's ok to dirty flash SRxx over SRxx. Just try it yourself and see if everything works fine on your device, if not, clean flash. You don't need posts of recommendation from other users for a no-brainer like that.