Men's college coach Ben Josephson discusses hand position for blockers. While coaches disagree about whether to use high hands or low hands, Josephson advocates for starting with low hands to quicken the blocker's footwork and maximize efficiency.
As Josephson says, everything in the game of volleyball is a give and take. A low hand position helps quicken the footwork and travel time to the pin block, but can result in a less-high block with the hands.
If the athlete starts with high hands, it results in a slower travel time which may result in a late block. Starting with high hands can also result in a slower jump loading, so starting with lower hands wastes less loading time.