Righto Tex, seeing nobody including the usually pedantic Giomen has roughed me up over Post #14, i'll stick my neck out a bit further and give you some more homework [test later, so pay attention]:

You'd be very familiar with rgn41 which is encrypted but in most units can be dumped to keep a 'non-vol' backup to restore if needed. 41 has all kinds of interesting and sensitive info in it such as UID and registration & unlock codes. If deleted, the unit will repopulate it but not fully. Codes can be forever lost for instance.

Apart from those already mentioned, other oft-used regions that can be [variously] dumped from modern units are 13, 15, 24, 34, 45, 83, 86, 91, 101, 127, 130, 132, 139, 140, 141, 142, 143, 150 & 154. Regions not mentioned are either empty, protected or don't exist afaik. The regions actually used and dumpable do vary and are differently used depending on series i.e. populated in some, empty on others. Maybe even protected or not depending on series too.

Region 83 in later devices [xx, 1xx, later 2/3xxx for example] is used for the file system in place of rgn48 which is used in earlier 2/4/7xx, 1/2/3xxx. If 48's used then 83 is empty and vice versa.

Region 140 can be manipulated in some modern units to unlock features otherwise blocked in firmware for certain models in a Series [e.g. [Only registered and activated users can see links. ] in a similar way that rgn16 [the logo] can be changed in some series to unlock features i.e. [Only registered and activated users can see links. ] and [Only registered and activated users can see links. ] for example. TTS can also be enabled in some 205/W, and HWID0827/0851 versions of 2x0W/2x0 can have traffic etc enabled by flashing a 'senior model logo' too: [Only registered and activated users can see links. ].

I'm unsure what those other regions' functions are specifically however, other than i think 34 has some quite sensitive functions and shouldn't be messed with at all and fw1_resources.bin is flashed to rgn127.
That should stop you looking for unicorns for a while .