Mixed thing, I believe, as sony uses different concepts. S-ON/S-OFF prevents flashing stuff using a custom recovery, correct?
I can give you information which I know from the Xperia T, a device which applies the same concepts as the Z. Everything which applies to the T will eventually, most likely, also apply to the Z once the exploits to obtain root are found.
Ok, so, a locked bootloader prevents you running custom kernels and an custom recoveries "natively", meaning on a locked device you cannot natively boot a custom recovery. It's comparable to S-ON I believe. On the T devs managed to circumvent this by obtaining root on a locked device and then used root acces to modify the chargemon script which is run upon booting the device to make it load a custom recovery additionally to it's intended function. The recovery is not flashed on a separate partition but deposited on /system as an archive. The script simply unpacks and loads it. Because the recovery runs with root permissions, you can then use it to flash stuff despite having a locked bootloader.
On an unlocked device, you can flash any compatible kernel and recovery and also natively boot them. An unlocked bootloader means full and unlimited access to the device.
Current:Sony XPERIA Z1 Compact (D5503) unlocked, rooted stock 4.4.4 | Asus Transformer Pad (TF300T) locked, rooted stock 4.3 Deprecated: Sony XPERIA Z, Sony XPERIA T, Samsung Galaxy S3, Samsung Galaxy Note, HTC DesireZ, HTC 7, Nokia N900, HTC Magic, HTC Touch Pro, SonyEricsson XPERIA X1, HTC Touch Cruise, HTC Canary (Orange SPV) et al.
Originally Posted by Ryland Johnson
It is clear that this phone has an awful lot more artificial intelligence than some of its owners.
XDA Developers was founded by developers, for developers. It is now a valuable resource for people who want to make the most of their mobile devices, from customizing the look and feel to adding new functionality. Are you a developer?