down slowly?

[KIB]

Hope this hasn't been covered too many times before. I just got the 5x5 e-book today (thanks Mehdi!) and noticed the bit about lifting tempo that says: "...lift fast. Apply maximal force to the bar while controlling the bar. Control the bar on the way down, but don’t make it slow." What is the difference between this approach and the "slow and steady" lift/down? I've seen a lot of advice recently to really slow down the "negative" (return/down) portion of the lift. People say it should take a count of 5-10 to really get a burn going. (Sorry that "people say" is pretty vague. I'll try to find a direct quote if it's important.) Thoughts on these two methods?
>edit
Okay, I'm finding more of Mehdi's articles about speed, especially for the lift. I can see it's just a different approach: high speed allows more weight, slower means... I'm not sure yet. I'll keep digging.
>edit
Now I've found Bass' "Lift Slow Or Say No" article, which lays things out nicely. It's linked at the bottom of Mehdi's "Should you lift super slow or super fast?" article which you can find from the e-book's FAQ. The Bass article.

[Mehdi]

Strength has different components. One of them is speed. More speed is more strength.
Think about this: you play soccer, you hit the ball hard. You play tennis you hit the bar hard. Barbell same thing: fast. Check weight lifters. Research also shows you're using more muscle fibers when lifting fast (cfr book practial programming for strength training by rippetoe or science & practice of strength training by zatsiorsky)