Originally Posted by prateekgujral
But flashing the rom clears all of these partitions anyway (system, cache and dalvik)
No, just flashing does not. You have to explicitly
clear Dalvik Cache or you'll have old stuff there once the new ROM loads up that will likely cause issues. Trust me, I learned the hard way
. (You can even read early posts in this thread, to see how I was claiming screen shot didn't work, till I learned to wipe properly.)
ROM Manager by default selects to clear Dalvik Cache when flashing a new ROM. But if you're not using ROM Manager and just doing it through a Recovery utility manually, Dalvik Cache is not cleared till you clear it.