S-OFF allows you many great things on HTC devices, such as the ability to flash unsigned modified code into protected partitions (ie. older hboots). It also allows switching between firmwares when a bad radio update is released, or you just want to go back to a ROM that was previously released (useful for devices like the HTC EVO 4G LTE when the ICS update broke Google Maps Navigation for seven months).
Getting S-OFF also allows you to flash carrier specific ROMs, the Google Play Edition ROM, etc.
For most at the moment S-OFF would mean you can get rid of the *TAMPERED* notice and red developer warning text when you boot the phones up and have unlocked and flashed an unsecure kernel.
If an unrooted device can achieve S-OFF, this means you would be able to S-OFF then root your phone without HTC ever getting your phone’s information or having to go through the pain of an unlock phone wipe that HTCDev puts you through.
S-OFF also means that HTC will probably be rushing to release a hastily patched together firmware update for any affected HBOOTs, so for those wanting to get the phone completely in their control, avoid taking any supposedly urgent firmware updates for a bit.
There is no information on when the exploit will be available, or if it’s carrier specific (probably not), or if there was a significant difference in launch day hboots and those released after, but I’ll keep looking for information on it as it comes out.
Let us know if you hear anything on this development and I’ll keep you posted if I hear anything.