There are so many reasons to go S-OFF.
Some are listed here:
xda-developers - View Single Post - [S-OFF]Development
One reason I like is that it lets me easily change CID and also not have to go through the whole HTCDev process of unlocking the bootloader, I could just type "fastboot oem unlock" and it's done. Going SuperCID also lets you install any RUU you want regardless of your region or model ID.
There are a lot of other reasons. If you don't feel that it is necessary for something specific, then you shouldn't really bother. I did it because I wanted to install a RUU and remove the tampered as well as "RELOCKED" statuses - with S-OFF you can restore the lock status to "locked" rather than "relocked" with S-ON.