I'm organizing a Texas Deadlift bar for PTC, I promised the guys if they hit certain deadlift goals, I'd get them one.
It's like doing a rack pull(kinda), you lift the bar 10cms(just a rough guess) or so before the plates even come off the ground, so that first 10cm is alot easier as you're not lifting the entire weight, also you can accelerate the bar alot harder, and carry that speed into the lockout, You're not lifting the full weight until the plates come off the ground, at which point you've already lifted the bar a fair distance.
Hope that helps.