Disclaimer: Not from personal experience
The most mind-blowing, intense, amazing, disgusting, intriguing, fascinating, revolting, deep, dark, mind-blowing (did I say that already?) and life-transforming body modification I can ever imagine. Yes, even more transforming than voluntary amputation or castration, IMHO.
The body is usually suspended on a rope pully system with multiple meat hooks that pierce the flesh. Some practitioners get their suspension points pierced with large gauge rings to lessen the damage to the flesh over time from repeated insertion of the hooks.
As with any mod, the motivation and experience sought from doing a flesh hook suspension varies between individuals. From my experience and reading, it appears that this isn't commonly done or seen within the BDSM/Kink/Leather community and is considered extreme, though an act deserving of grand respect among the Bod Mod community.
It's not something often done for eroticism. It's empowering. It's a flight ticket to another dimension. It's a challenge to one's body, endurance, limits, beliefs, eyes, mind, senses. It's a challenge even for onlookers. I'm personally amazed that skin is that strong. It encourages me to re-evaluate what my body is capable of.
Flesh Hook Suspension has a history that traces back thousands of years with roots in Hindu and Native American cultures. It's been performed for religious rites, divination, punishment, and rites of passage. Modern culture often challenges the sanity of those who choose to perform it in modern times, and try to disallow such acts from ever happening. That brings up the question of ownership of a body, and a person's right to do with their body as they see fit. I won't go off on a tangent with that. :)
Please, post your experiences here if you have any, or have witnessed one. Again, this is something I haven't personally experienced (though someday I might just pursue it) so I can only speak from an outsider's perspective, and I know that doesn't do it justice.