Whether you’re performing a deadlift or a snatch, the pull from the ground to the knees should be slow.
When a barbell is “dead” on the ground, it first must bend before being lifted. This is called the barbell whip. As weights continue to increase, so will the whip of the barbell.
Imagine putting 10-lb bumper plates on either end of a PVC pipe. As you pick it up from the ground, a hyperbola of sorts will form. If you lift it too fast, the weight will be jerked off the ground and displace your body.
Because of the barbell whip, the first pull of the clean and snatch need to be slow. Trying to lift weight fast off the ground will begin with the hips rising before the shoulders and end in a missed attempt forward.
Be patient in the first pull, you’re creating whip on the barbell. The power comes later when the hamstrings become engaged during the second pull.