I found it, i put this here for other people who don't know:
For those of you (like me) scratching your heads because you never heard of s-off:
In a nutshell, S-OFF means that the NAND portion of the device is unlocked and can be written to. The default setting for HTC’s devices is S-ON, which means that neither can you access certain areas of the system nor can you guarantee a permanent root. Furthermore, signature check for firmware images is also ensured by the S-ON flag.
How Do I Know If My Device Is S-ON Or S-OFF?
That is easy to verify. Simply boot into HBOOT on your device, and the text on top will show the flag status as either S-OFF or S-ON. A full root generally means S-OFF.
S-OFF – What And Why?
In their devices, HTC have installed a sort of security check whose level is determined by S-OFF/S-ON. Essentially, this security level is a flag stored on the device’s radio that checks signature images for any firmware before it is allowed to be written to system memory. This hinders using any custom ROMs, splash images, recovery etc., and also restricts access to the NAND flash memory. However, when security level is set to S-OFF, the signature check is bypassed, allowing a user to upload custom firmware images, unsigned boot, recovery, splash and HBOOT images, as well as official firmware that has been modified, this enabling maximum customization of your HTC Android device.
Furthermore, S-OFF also reduces restrictions on accessing the NAND flash memory on the device, allowing all partitions (including /system) to be mounted in write mode while the operating system is booted.
Thanks for the poster of this article since it isn't me who wrote this