For what it's worth, we in the Fiat Lux perform a Culee for our freshly stamped knights. (Those who witnessed Sir Jonathan's knighting a while back I'm sure remember/wince at the memory of Sir Barton's culee!) I find it rather important and memorable, as just about every member I've spoken with about it distinctly remembers theirs. (I chipped a tooth with mine. Barton's got quite the slap on 'im!)
One of the important things I think it symbolizes is the understanding of the mentor/mentored relationship. Though one is joining a peerage as an equal, there's still an unspoken chain of... not so much command as deference. One's sponsor is, in all things, their mentor. They're the one who brought them into knighthood, they're the one who taught them, raised them, educated them, and guided them. It's sort of the final test of trust and character - you know it's coming, and it's a sign of maturity, respect, and self-restraint to allow it to happen and embrace afterwards. I can't remember how many people shyed away from joining up because of the looming "threat" of the culee. When everything's said and done, though, it's just a capstone to a larger foundation of sacrifice, growth, and respect that was far longer, far more arduous, and endured for far greater gain.