What's the purpose in freezing grape cuttings?

I have never froze any of my cuttings, grape or otherwise, before rooting them. It is possible you have been given erroneous information; not everything you read online is true. My favorite ways to root grapes are either in pots while the vine is still attached or over winter after pruning. The first method is more labor-intense but generally produces better results. To use it, fill pots, buckets or other containers with potting soil or garden soil, elevate if necessary and support at a height that allows you to bury the rooting vine at a knuckle and at least 2 feet from the tip and leave throughout the summer and winter. In spring, before bud-break, cut the vine loose from the original vine and it is ready to be transplanted into its' new location. To help the rooting process you can carefully peel the outer layer of bark from the vine in the area to be buried. That gives a good location for the new roots to form. If planting the pruned ends you can peel them, too, just a short distance. No more than two knuckles and usually, just to the first knuckle. These will need to be kept moist, regardless of the method used, to help the roots form. Once rooted you can plant the new vines out to their new location.

Good luck and enjoy!

make that CHILL them..... to make them think they're going thru winter..... not freeze, which would kill them....