Whats with the box during the deadlift?

[Manuel]

Mark,
I was in the gym doing my 300 air squats for crossfit when I saw this guy doing deadlifts standing on a box. He had about 225# on the bar and the box must have been at least 3 to 4 inches in height. Does this serve a purpose?

P.S. thanks for signing the SS book my wife bought from you.

[Mark Rippetoe]

He was increasing the range of motion of the pull. It's mentioned in the book, which I was happy to sign for a deployed military guy. Thanks.