SSC means Safe, Sane, and Consensual. And that works well for many people playing around with BDSM. If those three terms are met then everything is fine.
However, for some people, SSC doesn't work so well with their kinks and fantasies and desires. One person's definition of insane is perfectly rational and sane to another. And one person's definition of safe may seem a bit too risky for someone else.
RACK stands for Risk Aware Consensual Kink. It acknowledges that much of what we do has some inherent risks. RACK acknowledges those risks and looks for ways to minimize them where possible. SSC says if it isn't safe you don't do it. RACK says we understand there may be a risk, but we've educated ourselves about it and know how to minimize the risks, and we choose to take the chance from an informed perspective. It's a different mindset.
With needle play and knife play there is risk of infection. With wax play and fire play there is risk of being burned. There are risks with electrical play, breath play, suspension bondage, watersports... the list goes on. Risk can be minimized with proper education, but there is still risk.
Why do people do it? Why take the risk? Personally, I think a big part of it has to do with the level of trust involved in taking things to that level. But that's not all of it - if you are turned on by bondage then five years from now you may need to take it to the next level to keep it fresh and new and still be turned on by it - that could mean suspension bondage.
And that leads me to talking about SSC versus RACK when it comes to erotica. Most of what I see in the popular consensual romantic BDSM books out there is SSC. But, most of those books are the beginning of a relationship, and often one of the partners is new to the scene. So SSC fits in with that basic template. But is that why most authors seem to stick to the tenets of SSC? Or is it that the readers are more comfortable with that?
There are a few edge activities that make it into books -- wax play, branding, and suspension bondage, for instance. But what about some of the less socially accepted, edgier, activities? Needle play? Breath control? Knife play? Fire play? Catheters? Would the extra risk, done responsibly, be more spice for you, or would it be a turn off?